Photomask, method for producing the same, and method for forming pattern using the photomask

ABSTRACT

A photomask has a semi-light-shielding portion having a light-shielding property and a light-transmitting portion surrounded by the semi-light-shielding portion, and a peripheral portion positioned in the periphery of the light-transmitting portion. The semi-light-shielding portion and the light-transmitting portion transmit exposure light in the same phase, whereas the peripheral portion transmits exposure light in a phase opposite to that of the light-transmitting portion.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a photomask for forming a finepattern used for producing a semiconductor integrated circuit device, amethod for producing the same and a method for forming a pattern usingthe photomask.

[0002] In recent years, it is increasingly necessary to miniaturizecircuit patterns for high integration of a large-scale integratedcircuit device (hereinafter, referred to as “LSI”) that can be realizedwith semiconductors. As a result, a reduction of the width of a line forwiring patterns constituting a circuit or miniaturization of contacthole patterns (hereinafter, referred to as “contact patterns”) thatconnect between layered wirings formed via insulating layers have becomevery important.

[0003] Hereinafter, miniaturization of wiring patterns with a recentlight-exposure system will be described by taking the case of using apositive resist process as an example. In a positive resist process, aline pattern refers to a line-shaped resist film (resist pattern) thatare left, corresponding to a non-exposed region of a resist by exposurewith a photomask and subsequent development. A space pattern refers to aportion from which a resist is removed (resist-removed pattern)corresponding to an exposed region of a resist. A contact pattern refersto a hole-like resist-removed portion and can be regarded as a smallspace pattern of the space patterns. When using a negative resistprocess instead of a positive resist process, the definition of the linepattern and the definition of the space pattern are replaced by eachother.

[0004] In general, for miniaturization of wiring patterns, a method forforming a fine line pattern with oblique incident light exposure(off-axis illumination) called super resolution exposure has been used.This method is an excellent method for miniaturization of a resistpattern corresponding to a non-exposed region of a resist, and also hasan effect of improving the depth of focus of dense patterns that arearranged periodically. However, this oblique incident exposure methodhas little effect on miniaturization of isolated resist-removedportions, and on the contrary, this method deteriorates the contrast ofimages (optical images) and the depth of focus. Therefore, the obliqueincident exposure method is positively used to form patternscharacterized in that the size of the resist-removed portion is largerthan the size of a resist pattern, for example, to form gate patterns.

[0005] On the other hand, to form a micro resist-removed portion that isisolated such as a small contact pattern, it is known that it is usefulto use a small light source having a low coherence degree that containsno oblique incident component. In this case, it is more useful to use ahalf-tone phase-shifting mask (see, for example, Japanese Laid-OpenPatent Publication No. 9-90601). In the half-tone phase-shifting mask, aphase sifter that has a very low transmittance of about 3 to 6% withrespect to exposure light and that causes phase inversion of 180 degreeswith respect to light transmitted through an opening, instead of acomplete light-shielding portion, is provided as a mask patternsurrounding a light-transmitting portion (opening) corresponding to acontact pattern.

[0006] In this specification, a transmittance is represented by aneffective transmittance when the transmittance of a transparentsubstrate is taken as 100%, unless otherwise specified. Moreover,“complete light-shielding film (complete light-shielding portion) refersto a light-shielding film (light-shielding portion) having an effectivetransmittance of smaller than 1%.

[0007] Hereinafter, the principle of the method for forming patternsusing a half-tone phase-shifting mask will be described with referenceto FIGS. 27A to 27G.

[0008]FIG. 27A is a plan view of a photomask in which an openingcorresponding to a contact pattern is provided in a chromium filmserving as a complete light-shielding portion provided on the surface ofthe mask. FIG. 27B shows the amplitude intensity corresponding to lineAA′ of light transmitted through the photomask shown in FIG. 27A. FIG.27C is a plan view of a photomask in which a chromium film correspondingto a contact pattern as a complete light-shielding portion is providedin a phase shifter provided on the surface of the mask. FIG. 27D showsthe amplitude intensity corresponding to line AA′ of light transmittedthrough the photomask shown in FIG. 27C. FIG. 27E is a plan view of aphotomask in which an opening corresponding to a contact pattern isprovided in a phase shifter provided on the surface of the mask (i.e., ahalf-tone phase-shifting mask). FIGS. 27F and 28G show the amplitudeintensity and the light intensity corresponding to line AA′ of lighttransmitted through the photomask shown in FIG. 27E, respectively.

[0009] As shown in FIGS. 27B, 27D, and 27F, the amplitude intensity oflight transmitted through the half-tone phase-shifting mask shown inFIG. 27E is equal to the sum of the amplitude intensities of lightstransmitted through the photomasks shown in FIGS. 27A and 27C. That isto say, in the half-tone phase-shifting mask shown in FIG. 27E, thephase shifter serving as a light-shielding portion is configured so asto not only transmit light at a low transmittance, but also provide anoptical path difference (phase difference) of 180 degrees with respectto the light transmitted through the opening to the light transmittedthrough this phase shifter. Therefore, as shown in FIGS. 27B and 27D,the light transmitted through the phase shifter has an amplitudeintensity with a phase opposite to that of the light transmitted throughthe opening. Thus, if the amplitude intensity distribution shown in FIG.27B and the amplitude intensity distribution shown in FIG. 27D aresynthesized, a phase boundary in which the amplitude intensity is turnedto 0 by a phase change is generated, as shown in FIG. 27F. As a result,as shown in FIG. 27G, in the end of the opening that is the phaseboundary (hereinafter, referred to as a “phase end”), the lightintensity, which is represented by a square of the amplitude intensity,becomes 0, and a significantly dark portion is formed. Accordingly, inan image of the light transmitted through the half-tone phase-shiftingmask shown in FIG. 27E, strong contrast is realized in the vicinity ofthe opening. However, the following should be noted: This improvement ofthe contrast occurs with respect to light vertically incident to themask, more specifically, that is, light incident to the mask from asmall light source region having a low coherence degree. However, thecontrast is not improved even in the vicinity of the opening (in thevicinity of the phase boundary in which a phase change occurs) withrespect to oblique incident exposure light, for example, exposure calledannular illumination in which a vertical incident component(illumination component from the center of a light source (the normaldirection of the mask) is removed. Furthermore, there is anotherdisadvantage in that compared with the case where exposure is performedwith a small light source having a low coherence degree, the depth offocus is lower in the case where oblique incident exposure is performed.

[0010] As described above, in order to form a fine resist-removedpattern such as a contact pattern using a positive resist process, itwas necessary to perform exposure with a small light source having acoherence degree of about 0.5 or less, which provides illumination onlywith vertical incident components, in combination with a half-tonephase-shifting mask. This method was very useful to form fine andisolated contact patterns.

[0011] There is a recent tendency associated with a high degree ofintegration of recent semiconductor devices that densely arrangedpatterns as well as isolated patterns are also required not only forwiring patterns but also contact patterns. In order to realize a highdepth of focus when forming densely arranged contact patterns, obliqueincident exposure is useful as in the case of the densely arrangedwiring patterns.

[0012] Furthermore, in recent years, also when forming wiring patterns,in addition to miniaturization of line patterns serving as wiringpatterns, there is an increasing demand for miniaturization of spacepatterns between wirings. As in the case of the isolated contactpatterns, it is useful to use a light source having a low coherencedegree in combination with a half-tone phase-shifting mask in order toform small isolated space patterns between wirings.

[0013] That is to say, although oblique incident exposure is essentialto form high density wiring patterns and high density contact patterns,the contrast and the depth of focus of isolated contact patterns andisolated space patterns between wirings are significantly deterioratedwhen oblique incident exposure is performed. The contrast and the depthof focus are deteriorated even more significantly when a half-tonephase-shifting mask is used to improve the resolution.

[0014] On the other hand, when a small light source having a lowcoherence degree is used to form small isolated contact patterns andsmall isolated space patterns between wirings, it becomes difficult toform high density patterns or small line patterns.

[0015] Therefore, the optimal illumination conditions with respect tosmall isolated space patterns and the optical illumination conditionswith respect to densely arranged patterns or small line patterns have acontradictory relationship. Therefore, in order to form small resistpatterns and small isolated resist-removed patterns at the same time, alight source having a medium coherence degree (about 0.5 to 0.6) is usedfor a trade-off between the effect of vertical incident components froma light source and the effect of oblique incident components from alight source. However, in this case, both the effect of verticalincident components and the effect of oblique incident components arecanceled, so that it is difficult to realize further high integration ofsemiconductor devices by miniaturizing isolated line patterns or denselyarranged patterns and isolated space patterns at the same time.

SUMMARY OF THE INVENTION

[0016] Therefore, with the foregoing in mind, it is an object of thepresent invention to miniaturize isolated space patterns and isolatedline patterns or dense patterns at the same time.

[0017] In order to achieve the above object, a first photomask of thepresent invention includes on a transparent substrate: asemi-light-shielding portion having a light-shielding property withrespect to exposure light: a light-transmitting portion surrounded bythe semi-light-shielding portion and having a light-transmittingproperty with respect to exposure light: and a peripheral portionsurrounded by the semi-light-shielding portion and positioned in aperiphery of the light-transmitting portion. The semi-light-shieldingportion and the light-transmitting portion transmit the exposure lightin the same phase. The peripheral portion transmits the exposure lightin a phase opposite to that of the semi-light-shielding portion and thelight-transmitting portion. The surface of the transparent substrate ina formation region for the light-transmitting portion is exposed. Afirst phase shift film that transmits the exposure light in a phaseopposite to that of the light-transmitting portion is formed on thetransparent substrate in a formation region for the peripheral portion.The first phase shift film and a second phase shift film that transmitsthe exposure light in a phase opposite to that of the light-transmittingportion are laminated sequentially on the transparent substrate in aformation region for the semi-light-shielding portion. A multilayeredstructure of the first phase shift film and the second phase shift filmhas a transmittance that allows the exposure light to be transmittedpartially and transmits the exposure light in the same phase as that ofthe light-transmitting portion.

[0018] According to the first photomask, a peripheral portion thattransmits exposure light in a phase opposite to that of alight-transmitting portion is sandwiched by the light-transmittingportion and a semi-light-shielding portion having a light-shieldingproperty that transmits the exposure light in the same phase as that ofthe light-transmitting portion. As a result, the contrast in the lightintensity distribution between the light-transmitting portion and theperipheral portion can be enhanced by mutual interference between thelight transmitted through the light-transmitting portion and the lighttransmitted through the peripheral portion. This contrast enhancementeffect also can be obtained when a fine isolated resist-removed portion(i.e., a fine isolated space pattern corresponding to thelight-transmitting portion) is formed with oblique incident exposure(off-axis illumination), for example, in the positive resist process.That is to say, it is possible to miniaturize isolated space patternsand isolated line patterns or dense patterns at the same time bycombining the first photomask and oblique incident exposure.

[0019] Furthermore, according to the first photomask, the transmittanceof the peripheral portion can be defined by the single layered structureof the first phase shift film, and the transmittance of thesemi-light-shielding portion can be defined by the multilayeredstructure of the first phase shift film and the second phase shift film,so that a combination of the transmittance of the peripheral portion andthe semi-light-shielding portion can be set arbitrarily.

[0020] In this specification, “having light-transmitting properties withrespect to exposure” means having a transmittance that allows a resistto be exposed, and “having light-shielding properties with respect toexposure” means having a transmittance that does not allow a resist tobe exposed. The “same phase” means a phase difference of (−30+360×n)degrees or more and (30+360×n) degrees or less, (where n=an integer),and the “opposite phase” means a phase difference of (150+360×n) degreesor more and (210+360×n) degrees or less.

[0021] In the first photomask, it is preferable that the first phaseshift film has a first transmittance adjusting film and a first phaseadjusting film formed on the first transmittance adjusting film, thefirst transmittance adjusting film transmits the exposure light in thesame phase as that of the light-transmitting portion and has arelatively low transmittance with respect to the exposure light, and thefirst phase adjusting film transmits the exposure light in a phaseopposite to that of the light-transmitting portion and has a relativelyhigh transmittance with respect to the exposure light.

[0022] With this embodiment, a combination of a desired phase differenceand a desired transmittance can be selected arbitrarily for the firstphase shift film, and a combination of the material of the transmittanceadjusting film and the material of the phase adjusting film makes itpossible to improve the selection ratio at etching for processing thefirst phase shift film.

[0023] In the first photomask, it is preferable that the second phaseshift film has a second transmittance adjusting film and a second phaseadjusting film formed on the second transmittance adjusting film, thesecond transmittance adjusting film transmits the exposure light in thesame phase as that of the light-transmitting portion and has arelatively low transmittance with respect to the exposure light, and thesecond phase adjusting film transmits the exposure light in a phaseopposite to that of the light-transmitting portion and has a relativelyhigh transmittance with respect to the exposure light.

[0024] With this embodiment, a combination of a desired phase differenceand a desired transmittance can be selected arbitrarily for the secondphase shift film, and a combination of the material of the transmittanceadjusting film and the material of the phase adjusting film makes itpossible to improve the selection ratio at etching for processing thesecond phase shift film.

[0025] In the first photomask, the peripheral portion may be in contactwith the light-transmitting portion or may be spaced apart from thelight-transmitting portion by a predetermined distance.

[0026] In the first photomask, it is preferable that the first phaseshift film has a first phase adjusting film that transmits the exposurelight in a phase opposite to that of the light-transmitting portion, thesecond phase shift film has a second phase adjusting film that is formedon the first phase adjusting film and transmits the exposure light in aphase opposite to that of the light-transmitting portion, and atransmittance adjusting film having a lower transmittance than that ofthe phase adjusting films with respect to the exposure light is formedbetween the first phase adjusting film and the second phase adjustingfilm.

[0027] With this embodiment, the semi-light-shielding portion has astructure in which a transmittance adjusting film having a lowtransmittance is provided between the first phase adjusting film and thesecond phase adjusting film, and therefore the difference intransmittance between the semi-light-shielding portion and theperipheral portion can be increased, so that the contrast in the lightintensity distribution between the light-transmitting portion and theperipheral portion can be enhanced more. Furthermore, when the structurein which the transmittance adjusting film is formed partially on thefirst phase adjusting film in the peripheral portion formation region isused, the effective transmittance of the peripheral portion can beadjusted finely by the area ratio of the peripheral portion that iscovered with the transmittance adjusting film (=(the area of thetransmittance adjusting film in the peripheral portion formationregion)/(the area of the peripheral portion)). Therefore, it is possibleto arbitrarily change the transmittance of the peripheral portiondepending on the pattern shape on the same photomask.

[0028] In the photomask, it is preferable that the transmittance of thesemi-light-shielding portion with respect to the exposure light is 6% ormore and 15% or less.

[0029] With this embodiment, the contrast enhancement effect by thefirst photomask can be obtained reliably while preventing a reduction inthickness of the resist film in pattern formation.

[0030] A second photomask of the present invention includes on atransparent substrate: a semi-light-shielding portion having alight-shielding property with respect to exposure light: alight-transmitting portion surrounded by the semi-light-shieldingportion and having a light-transmitting property with respect toexposure light: and a peripheral portion surrounded by thesemi-light-shielding portion and positioned in a periphery of thelight-transmitting portion. The semi-light-shielding portion and thelight-transmitting portion transmit the exposure light in the samephase. The peripheral portion transmits the exposure light in a phaseopposite to that of the semi-light-shielding portion and thelight-transmitting portion. The surface of the transparent substrate ina formation region for the light-transmitting portion is exposed. Asemi-light-shielding film that has a transmittance allowing the exposurelight to be transmitted partially and transmits the exposure light inthe same phase to that of the light-transmitting portion is formed onthe transparent substrate in the semi-light-shielding portion formationregion. The semi-light-shielding film with a reduced thickness is formedon the transparent substrate in a formation region for the peripheralportion, the thickness being such an extent that the exposure light istransmitted in a phase opposite to that of the light-transmittingportion.

[0031] According to the second photomask, a peripheral portion thattransmits exposure light in a phase opposite to that of alight-transmitting portion is sandwiched by the light-transmittingportion and a semi-light-shielding portion having a light-shieldingproperty that transmits the exposure light in the same phase as that ofthe light-transmitting portion. As a result, the contrast in the lightintensity distribution between the light-transmitting portion and theperipheral portion can be enhanced by mutual interference between thelight transmitted through the light-transmitting portion and the lighttransmitted through the peripheral portion. This contrast enhancementeffect also can be obtained when a fine isolated resist-removed portion(i.e., a fine isolated space pattern corresponding to thelight-transmitting portion) is formed with oblique incident exposure,for example, in the positive resist process. That is to say, it ispossible to miniaturize isolated space patterns and isolated linepatterns or dense patterns at the same time by combining the secondphotomask and oblique incident exposure.

[0032] Furthermore, according to the second photomask, thesemi-light-shielding portion is constituted by a single layeredstructure of the semi-light-shielding film, so that the mask structureis very simple. Moreover, a peripheral portion can be formed easilysimply by partially reducing the thickness of the semi-light-shieldingfilm, in other words, by providing a recess in the light-shielding film.Furthermore, also in the case where a semi-light-shielding portionhaving a small width is present between the peripheral portion and thelight-transmitting portion, peeling of the film constituting thesemi-light-shielding portion having a small width can be suppressed,compared with the case where a semi-light-shielding portion of amultilayered film structure is used.

[0033] In the second photomask, it is preferable that thesemi-light-shielding film has a transmittance adjusting film formed onthe transparent substrate and a phase adjusting film formed on thetransmittance adjusting film. The transmittance adjusting film transmitsthe exposure light in the same phase as that of the light-transmittingportion and has a relatively low transmittance with respect to theexposure light, and the phase adjusting film has a relatively hightransmittance with respect to the exposure light. The phase adjustingfilm in a formation region for the semi-light-shielding portion has athickness that transmits the exposure light in the same phase as that ofthe light-transmitting portion. The phase adjusting film in a formationregion for the peripheral portion has a thickness that transmits theexposure light in a phase opposite to that of the light-transmittingportion.

[0034] With this embodiment, a combination of a desired phase differenceand a desired transmittance can be selected arbitrarily for thesemi-light-shielding film, and a combination of the material of thetransmittance adjusting film and the material of the phase adjustingfilm makes it possible to improve the selection ratio at etching forprocessing the semi-light-shielding film.

[0035] In the second photomask, it is preferable that thesemi-light-shielding film has a phase adjusting film formed on thetransparent substrate and a transmittance adjusting film formed only onthe phase adjusting film in the semi-light-shielding portion formationregion, the transmittance adjusting film transmits the exposure light inthe same phase as that of the light-transmitting portion and has arelatively low transmittance with respect to the exposure light, thephase adjusting film has a relatively high transmittance with respect tothe exposure light, the phase adjusting film in a formation region forthe semi-light-shielding portion has a thickness that transmits theexposure light in the same phase as that of the light-transmittingportion, and the phase adjusting film in a formation region for theperipheral portion has a thickness that transmits the exposure light ina phase opposite to that of the light-transmitting portion.

[0036] With this embodiment, a combination of a desired phase differenceand a desired transmittance can be selected arbitrarily for thesemi-light-shielding film, and a combination of the material of thetransmittance adjusting film and the material of the phase adjustingfilm makes it possible to improve the selection ratio at etching forprocessing the semi-light-shielding film.

[0037] In the second photomask, the peripheral portion may be in contactwith the light-transmitting portion or may be spaced apart from thelight-transmitting portion by a predetermined distance.

[0038] In the second photomask, it is preferable that the transmittanceof the semi-light-shielding portion with respect to the exposure lightis 6% or more and 15% or less.

[0039] With this embodiment, the contrast enhancement effect by thesecond photomask can be obtained reliably while preventing a reductionin thickness of the resist film in pattern formation.

[0040] A third photomask of the present invention include on atransparent substrate: a semi-light-shielding portion having alight-shielding property with respect to exposure light: alight-transmitting portion surrounded by the semi-light-shieldingportion and having a light-transmitting property with respect toexposure light: and a peripheral portion surrounded by thesemi-light-shielding portion and positioned in a periphery of thelight-transmitting portion. The semi-light-shielding portion and thelight-transmitting portion transmit the exposure light in the samephase. The peripheral portion transmits the exposure light in a phaseopposite to that of the semi-light-shielding portion and thelight-transmitting portion. The surface of the transparent substrate ina formation region for the light-transmitting portion is exposed. Asemi-light-shielding film that has a transmittance that allows theexposure light to be transmitted partially and transmits the exposurelight in the same phase as that of the light-transmitting portion isformed on the transparent substrate in the semi-light-shielding portion.The transparent substrate in a formation region for the peripheralportion is dug down so as to have a thickness that transmits theexposure light in a phase opposite to that of the light-transmittingportion.

[0041] According to the third photomask, a peripheral portion thattransmits exposure light in a phase opposite to that of alight-transmitting portion is sandwiched by the light-transmittingportion and a semi-light-shielding portion having a light-shieldingproperty that transmits the exposure light in the same phase as that ofthe light-transmitting portion. As a result, the contrast in the lightintensity distribution between the light-transmitting portion and theperipheral portion can be enhanced by mutual interference between thelight transmitted through the light-transmitting portion and the lighttransmitted through the peripheral portion. This contrast enhancementeffect also can be obtained when a fine isolated resist-removed portion(i.e., a fine isolated space pattern corresponding to thelight-transmitting portion) is formed with oblique incident exposure,for example, in the positive resist process. That is to say, it ispossible to miniaturize isolated space patterns and isolated linepatterns or dense patterns at the same time by combining the thirdphotomask and oblique incident exposure.

[0042] Furthermore, according to the third photomask, thesemi-light-shielding portion is constituted by a single layeredstructure of the semi-light-shielding film, so that the mask structureis very simple.

[0043] In the third photomask, it is preferable that thesemi-light-shielding film has a transmittance adjusting film formed onthe transparent substrate and a phase adjusting film formed on thetransmittance adjusting film, the transmittance adjusting film has arelatively low transmittance with respect to the exposure light, and thephase adjusting film has a relatively high transmittance with respect tothe exposure light.

[0044] With this embodiment, a combination of a desired phase differenceand a desired transmittance can be selected arbitrarily for thesemi-light-shielding film, and a combination of the material of thetransmittance adjusting film and the material of the phase adjustingfilm makes it possible to improve the selection ratio at etching forprocessing the semi-light-shielding film.

[0045] In the third photomask, the peripheral portion may be in contactwith the light-transmitting portion or may be spaced apart from thelight-transmitting portion by a predetermined distance.

[0046] In the third photomask, it is preferable that the transmittanceof the semi-light-shielding portion with respect to the exposure lightis 6% or more and 15% or less.

[0047] With this embodiment, the contrast enhancement effect by thethird photomask can be obtained reliably while preventing a reduction inthickness of the resist film in pattern formation.

[0048] A method for forming a pattern of the present invention, whichuses either one of the first to the third photomasks, includes the stepsof: forming a resist film on a substrate; irradiating the resist filmwith the exposure light via the photomask, and developing the resistfilm irradiated with the exposure light so as to pattern the resistfilm.

[0049] According to the method for forming a pattern of the presentinvention, the same effects as those of the first to the thirdphotomasks of the present invention can be obtained. The above effectscan be obtained reliably by using off-axis illumination (obliqueincident exposure) in the step of irradiating the resist film with theexposure light.

[0050] A first method for producing a photomask of the present inventionis a method for producing the photomask including a semi-light-shieldingportion having a light-shielding property with respect to exposurelight: a light-transmitting portion surrounded by thesemi-light-shielding portion and having a light-transmitting propertywith respect to exposure light: and a peripheral portion surrounded bythe semi-light-shielding portion and positioned in a periphery of thelight-transmitting portion on a transparent substrate. Morespecifically, the method includes a first step of forming a first phaseshift film that transmits the exposure light in a phase opposite to thatof the light-transmitting portion on the transparent substrate, and asecond step of forming a second phase shift film that transmits theexposure light in a phase opposite to that of the light-transmittingportion on the first phase shift film, a third step of removing thesecond phase shift film in a formation region for the light-transmittingportion and a formation region for the peripheral portion, and a fourthstep of removing the first phase shift film in the light-transmittingportion formation region after the third step. A multilayered structureof the first phase shift film and the second phase shift film formed onthe transparent substrate in the semi-light-shielding portion formationregion has a transmittance that allows the exposure light to betransmitted partially and transmits the exposure light in the same phaseas that of the light-transmitting portion.

[0051] According to the first method for producing a photomask, thefirst and the second phase shift films that transmit exposure light witha phase inversion are formed sequentially on the transparent substrate.Then, the second phase shift film in the light-transmitting portionformation region and the peripheral portion formation region is removed.Thereafter, the first phase shift film in the light-transmitting portionformation region is removed. That is to say, the light-transmittingportion is made of the exposed portion of the transparent substrate, andthe semi-light-shielding portion is made of a multilayered structure ofthe first phase shift film and the second phase shift film. Theperipheral portion is made of a single layered structure of the firstphase shift film. The multilayered structure of the first and the secondphase shift films transmits exposure light in the same phase as that ofthe light-transmitting portion. Therefore, the peripheral portion thattransmits exposure light in the phase opposite to that of thelight-transmitting portion is sandwiched by the light-transmittingportion and the semi-light-shielding portion that transmits exposurelight in the same phase as that of the light-transmitting portion. As aresult, the contrast in the light intensity distribution between thelight-transmitting portion and the peripheral portion can be enhanced bymutual interference between the light transmitted through thelight-transmitting portion and the light transmitted through theperipheral portion. This contrast enhancement effect also can beobtained when a fine isolated resist-removed portion (i.e., a fineisolated space pattern corresponding to the light-transmitting portion)is formed with oblique incident exposure, for example, in the positiveresist process. That is to say, it is possible to miniaturize isolatedspace patterns and isolated line patterns or dense patterns at the sametime with oblique incident exposure.

[0052] According to the first method for producing a photomask, thefirst and the second phase shift films that are laminated on thetransparent substrate are etched selectively, so that a mask patternwith any shape that has the semi-light-shielding portion and theperipheral portion can be easily realized.

[0053] Furthermore, according to the first method for producing aphotomask, when the light-transmitting portion and the peripheralportion are apart, in other words, when a semi-light-shielding portionmade of the multilayered structure of the first and the second phaseshift films is present between the light-transmitting portion and theperipheral portion, the first phase shift film can be etched in aself-alignment manner, using the patterned second phase adjusting filmas a mask. Therefore, photomask process can be performed precisely.

[0054] A second method for producing a photomask of the presentinvention is a method for producing the photomask including asemi-light-shielding portion having a light-shielding property withrespect to exposure light: a light-transmitting portion surrounded bythe semi-light-shielding portion and having a light-transmittingproperty with respect to exposure light: and a peripheral portionsurrounded by the semi-light-shielding portion and positioned in aperiphery of the light-transmitting portion on a transparent substrate.More specifically, the method includes a first step of forming a firstphase shift film that transmits the exposure light in a phase oppositeto that of the light-transmitting portion on the transparent substrate,and a second step of forming a second phase shift film that transmitsthe exposure light in a phase opposite to that of the light-transmittingportion on the first phase shift film, a third step of removing thesecond phase shift film in a formation region for the peripheralportion, and a fourth step of removing the second phase shift film andthe first phase shift film in the light-transmitting portion formationregion sequentially after the third step. In a multilayered structure ofthe first phase shift film and the second phase shift film formed on thetransparent substrate in the semi-light-shielding portion formationregion has a transmittance that allows the exposure light to betransmitted partially and transmits the exposure light in the same phaseas that of the light-transmitting portion.

[0055] According to the second method for producing a photomask, thefirst and the second phase shift films that transmit exposure light witha phase inversion are formed sequentially on the transparent substrate.Then, the second phase shift film in the peripheral portion formationregion is removed. Thereafter, the second phase shift film and the firstphase shift film in the light-transmitting portion formation region areremoved. That is to say, the light-transmitting portion is made of theexposed portion of the transparent substrate, and thesemi-light-shielding portion is made of a multilayered structure of thefirst phase shift film and the second phase shift film. The peripheralportion is made of a single layered structure of the first phase shiftfilm. The multilayered structure of the first and the second phase shiftfilms transmits exposure light in the same phase as that of thelight-transmitting portion. Therefore, the peripheral portion thattransmits exposure light in the phase opposite to that of thelight-transmitting portion is sandwiched by the light-transmittingportion and the semi-light-shielding portion that transmits exposurelight in the same phase as that of the light-transmitting portion.Therefore, the contrast in the light intensity distribution between thelight-transmitting portion and the peripheral portion can be enhanced bymutual interference between the light transmitted through thelight-transmitting portion and the light transmitted through theperipheral portion. This contrast enhancement effect also can beobtained when a fine isolated resist-removed portion (i.e., a fineisolated space pattern corresponding to the light-transmitting portion)is formed with oblique incident exposure, for example, in the positiveresist process. That is to say, it is possible to miniaturize isolatedspace patterns and isolated line patterns or dense patterns at the sametime with oblique incident exposure.

[0056] According to the second method for producing a photomask, thefirst and the second phase shift films that are laminated on thetransparent substrate are etched selectively, so that a mask patternwith any shape that has the semi-light-shielding portion and theperipheral portion can be easily realized.

[0057] Furthermore, according to the second method for producing aphotomask, the step of removing the second phase shift film in theperipheral portion formation region and the step of removing the secondphase shift film in the light-transmitting portion formation region areperformed separately. Therefore, when the light-transmitting portion andthe peripheral portion are apart by a small distance, in other words,when the semi-light-shielding portion having a small width made of themultilayered structure of the first and the second phase shift films ispresent between the light-transmitting portion and the peripheralportion, the margin for photomask processing is increased.

[0058] In the first and the second methods for producing a photomask, itis preferable that the transmittance of the semi-light-shielding portionwith respect to the exposure light is 6% or more and 15% or less.

[0059] With this embodiment, the contrast enhancement effect by thefirst and the second methods for producing a photomask can be obtainedreliably while preventing a reduction in thickness of the resist film inpattern formation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0060]FIGS. 1A to 1G are diagrams illustrating the principle of theoutline enhancement method of the present invention.

[0061]FIGS. 2A to 2F are diagrams illustrating the dependence of theconventional image enhancement effect utilizing a phase end on the shapeof a light source.

[0062]FIGS. 3A to 3F are diagrams illustrating the limit of the size ofa phase shifter in the outline enhancement method of the presentinvention.

[0063]FIGS. 4A and 4B are diagrams illustrating the limit of the size ofa phase shifter in the outline enhancement method of the presentinvention.

[0064]FIGS. 5A to 5F are diagrams illustrating the light intensitydistribution produced by exposure light incident from various lightsource positions in forming isolated patterns with an outlineenhancement mask of the present invention.

[0065]FIGS. 6A to 6F are diagrams illustrating the light intensitydistribution produced by exposure light incident from various lightsource positions in forming isolated patterns with a conventionalhalf-tone phase-shifting mask.

[0066]FIGS. 7A to 7F are diagrams illustrating the dependence of thecontrast and the DOF on the transmittance of a semi-light shieldingportion in the outline enhancement mask of the present invention.

[0067]FIGS. 8A to 8F are diagrams illustrating variations of the layoutof a light shielding mask patterns constituted by a semi-light shieldingportion and a phase shifter in the outline enhancement mask providedwith an opening corresponding to a contact pattern.

[0068]FIG. 9A shows a view showing an example of a desired pattern to beformed with a photomask of a first embodiment of the present invention.FIG. 9B is a plan view of the photomask of the first embodiment of thepresent invention. FIG. 9C is a cross-sectional view taken along lineAA′ in FIG. 9B.

[0069]FIG. 10A is a cross-sectional view of the photomask of the firstembodiment of the present invention in which each of a lower phaseshifter and an upper phase shifter is a single layered film. FIG. 10B isa cross-sectional view of the photomask of the first embodiment of thepresent invention in which each of a lower phase shifter and an upperphase shifter is a multilayered film of a transmittance adjusting filmand a phase adjusting film.

[0070]FIG. 11A is a view showing the shape of a regular exposure lightsource. FIG. 11B is a view showing the shape of an annular exposurelight source. FIG. 11C is a view showing the shape of a quadrupoleexposure light source. FIG. 11D is a view showing the shape of anannular-quadrupole mixed type exposure light source.

[0071]FIGS. 12A to 12D are cross-sectional views showing the processesof a method forming a pattern with the photomask of the first embodimentof the present invention.

[0072]FIGS. 13A to 13E are cross-sectional views showing the processesof a method producing the photomask of the first embodiment of thepresent invention. FIG. 13F is a plan view corresponding to thecross-sectional view of FIG. 13C, and FIG. 13G is a plan viewcorresponding to the cross-sectional view of FIG. 13E.

[0073]FIGS. 14A to 14E are cross-sectional views showing the processesof a method producing the photomask of a first variation of the firstembodiment of the present invention. FIG. 14F is a plan viewcorresponding to the cross-sectional view of FIG. 14C, and FIG. 14G is aplan view corresponding to the cross-sectional view of FIG. 14E.

[0074]FIGS. 15A to 15E are cross-sectional views showing the processesof a method producing the photomask of a second variation of the firstembodiment of the present invention. FIG. 15F is a plan viewcorresponding to the cross-sectional view of FIG. 15C, and FIG. 15G is aplan view corresponding to the cross-sectional view of FIG. 15E.

[0075]FIG. 16A is a view showing an example of a desired pattern to beformed with the photomask of a second embodiment of the presentinvention. FIG. 16B is a plan view of the photomask of the secondembodiment of the present invention. FIG. 16C is a cross-sectional viewtaken along line AA′ of FIG. 16B.

[0076]FIGS. 17A to 17D are cross-sectional views showing the processesof a method forming a pattern with the photomask of the secondembodiment of the present invention.

[0077]FIGS. 18A to 18D are views showing variations of thecross-sectional structure of the photomask of the second embodiment ofthe present invention.

[0078]FIG. 19A is a view showing an example of a desired pattern to beformed with the photomask of a third embodiment of the presentinvention. FIG. 19B is a plan view of the photomask of the thirdembodiment of the present invention. FIG. 19C is a cross-sectional viewtaken along line AA′ of FIG. 19B.

[0079]FIGS. 20A to 20D are cross-sectional views showing the processesof a method forming a pattern with the photomask of the third embodimentof the present invention.

[0080]FIGS. 21A and 21B are a plan view and a cross-sectional view ofthe photomask of the third embodiment of the present invention in whicha thin portion of a half-tone film is in contact with an opening,respectively. FIGS. 21C and 21D are a plan view and a cross-sectionalview of the photomask of the third embodiment of the present inventionin which a thin portion of a half-tone film is apart from an opening bya predetermined distance, respectively.

[0081]FIG. 22A is a view showing an example of a desired pattern to beformed with the photomask of a fourth embodiment of the presentinvention. FIG. 22B is a plan view of the photomask of the fourthembodiment of the present invention. FIG. 22C is a cross-sectional viewtaken along line AA′ of FIG. 22B.

[0082]FIGS. 23A to 23D are cross-sectional views showing the processesof a method forming a pattern with the photomask of the fourthembodiment of the present invention.

[0083]FIGS. 24A to 24E are cross-sectional views showing the processesof a method producing the photomask of the fourth embodiment of thepresent invention. FIG. 24F is a plan view corresponding to thecross-sectional view of FIG. 24C, and FIG. 24G is a plan viewcorresponding to the cross-sectional view of FIG. 24E.

[0084]FIGS. 25A to 25C are diagrams illustrating an influence of a phasechange due to a light-shielding portion with a reduced thickness beingused as the semi-light-shielding portion of the photomask of the fourthembodiment on the pattern formation.

[0085]FIG. 26A is a plan view of the photomask of the fourth embodimentof the present invention in which a dug portion in a transparentsubstrate is apart from an opening by a predetermined distance. FIGS.26B to 26D are cross-sectional views in this case.

[0086]FIGS. 27A to 27G are diagrams illustrating the image enhancementprinciple with a conventional half-tone phase-shifting mask.

DETAILED DESCRIPTION OF THE INVENTION

[0087] First, a method for improving the resolution with the photomaskinvented by the inventors of the present application to realize thepresent invention, more specifically, an “outline enhancement method” toimprove the resolution of isolated space patterns will be describedbelow.

[0088] Outline Enhancement Method

[0089] Hereinafter, the outline enhancement method will be described bytaking formation of contact patterns by a positive resist process as anexample. The “outline enhancement method” is a principle that can beused for any patterns, regardless of its shape, as long as the patternsare small space patterns in a positive resist process. Furthermore, the“outline enhancement method” can be applied to a negative resist processtotally in the same manner, if the small space patterns (resist-removedpatterns) in the positive resist process are replaced by small patterns(resist patterns).

[0090]FIGS. 1A to 1G are diagrams illustrating the principle to enhancethe contract of transferred images of light in exposure for formingcontact patterns.

[0091]FIG. 1A is a plan view of a photomask in which an opening (i.e.,light-transmitting portion) corresponding to a contact pattern issurrounded by a semi-light-shielding portion having a transmittance of6% or more and 15% or less with respect to exposure light. FIG. 1B showsthe amplitude intensity corresponding to line AA′ of light transmittedthrough the photomask shown in FIG. 1A.

[0092]FIG. 1C is a plan view of a photomask in which a phase shifter isdisposed in a peripheral area of the opening shown in FIG. 1A, and acomplete light-shielding portion is disposed in the other area. FIG. 1Dshows the amplitude intensity corresponding to line AA′ of lighttransmitted through the photomask shown in FIG. 1C. The amplitudeintensity of light shown in FIG. 1D is that of the light transmittedthrough a phase shifter, and therefore this amplitude intensity has anopposite phase with respect to the amplitude intensity of light shown inFIG. 1B.

[0093]FIG. 1E is a plan view of a photomask in which an openingcorresponding to a contact pattern and a phase shifter disposed in theperipheral area of the opening are surrounded by a semi-light-shieldingportion having a transmittance of 6% or more and 15% or less withrespect to exposure light. FIGS. 1F and 1G are the amplitude intensityand the light intensity (a square of the amplitude intensity of light)corresponding to line AA′ of light transmitted through the photomaskshown in FIG. 1E. The photomask shown in FIG. 1E is a photomask obtainedby disposing a phase shifter in a peripheral area of the opening in thephotomask shown in FIG. 1A. The photomask shown in FIG. 1E is an exampleof the photomask of the present invention that can realize the outlineenhancement method (hereinafter, referred to as “outline enhancementmask”).

[0094] The photomask shown in FIG. 1A or 1E, the light transmittedthrough the semi-light shielding portion and the light transmittedthrough the opening have the same phase (more specifically, a phasedifference of (−30+360×n) degrees or more and (30+360×n) degrees orless, where n=an integer). In the photomask shown in FIG. 1E, the lighttransmitted through the phase shifter and the light transmitted throughthe opening have opposite phases (more specifically, a phase differenceof (150+360×n) degrees or more and (210+360×n) degrees or less, wheren=an integer).

[0095] The principle based on which transferred image of lighttransmitted through the outline enhancement mask shown in FIG. 1E is asfollows. The structure of the photomask shown in FIG. 1E is a structurein which the photomasks shown in FIGS. 1A and 1C are overlapped eachother. Therefore, as shown in FIGS. 1B, 1D, and 1F, the amplitudeintensity of light transmitted through the photomask shown in FIG. 1Ehas a distribution similar to that obtained by overlapping the amplitudeintensities of the lights transmitted through the photomasks shown inFIGS. 1A and 1C. As seen from FIG. 1F, in the photomask shown in FIG.1E, if the intensity of light transmitted through the phase shifterdisposed in the periphery of the opening can cancel a part of each ofthe lights transmitted through the opening and the semi-light shieldingportion. Therefore, in the photomask shown in FIG. 1E, if the intensityof the light transmitted through the phase shifter is adjusted such thatlight in the periphery of the opening is canceled, it is possible toform a light intensity distribution in which the light intensitycorresponding to the periphery of the opening is reduced to nearly 0, asshown in FIG. 1G.

[0096] In the photomask shown in FIG. 1E, the light transmitted throughthe phase shifter cancels the light in the periphery of the opening to ahigh degree, but cancels the light in the vicinity of the center of theopening to a low degree. As a result, there is another advantage thatthe slope of the profile of the light intensity distribution of thelight transmitted through the photomask shown in FIG. 1E in which thelight intensity changes from the center of the opening to the peripheryof the opening is increased, as shown in FIG. 1G. Therefore, the lightintensity distribution of the light transmitted through the photomaskshown in FIG. 1E has a sharp profile, so that images having a highcontrast can be formed.

[0097] Above described is the principle based on which optical images(images of light intensity) in the present invention are enhanced. Inother words, a phase shifter is disposed along the outline of an openingin a mask formed of a semi-light shielding portion having a lowtransmittance, so that it is possible to form a very dark portioncorresponding to the outline of the opening in a light intensity imageformed with the photomask shown in FIG. 1A. Thus, a light intensitydistribution in which the contrast between the light intensity in theopening and the light intensity in the periphery of the opening isenhanced can be formed. In this specification, a method by which imageenhancement is performed based on this principle is referred to as the“outline enhancement method”, and the photomask that realizes thisprinciple is referred to as an “outline enhancement mask”.

[0098] Hereinafter, the difference between the outline enhancementmethod, which is the basic principle of the present invention, and theprinciple of a conventional method using a half-tone phase-shifting maskwill be described. The most important point of the principle of theoutline enhancement mask is that a part of the light transmitted througheach of the semi-light shielding portion and the opening is canceled bythe light transmitted through the phase shifter, so that a dark portionis formed in the light intensity distribution, that is, that the phaseshifter behaves in a manner similar to a non-transparent pattern (opaquepattern). Therefore, as shown in FIG. 1F, a dark portion is formed by achange in intensity on the same phase side in the amplitude intensity ofthe light transmitted through the outline enhancement mask. Only in thisstate, the contrast can be improved by oblique incident exposure, whichwill be described in detail later.

[0099] On the other hand, also in the light intensity distributionobtained by exposure with the conventional half-tone phase-shifting maskhaving an opening corresponding to a contact pattern, a very darkportion is formed in the periphery of the opening, as shown in FIG. 27G.However, when the amplitude intensity of the light shown in FIG. 27Fobtained by exposure with the half-tone phase-shifting mask is comparedwith the amplitude intensity of the light shown in FIG. 1F obtained byexposure with the outline enhancement mask, the following difference isclearly present. As shown in FIG. 27F, in the amplitude intensitydistribution obtained by exposure with the half-tone phase-shiftingmask, a phase boundary in which a phase inversion occurs is present. Asshown in FIG. 27G, this phase boundary constitutes a dark portion of thelight intensity distribution due to the phase end and thus imageenhancement is realized. However, in order to form a dark portion due tothe phase end to obtain an enhancement effect of the contract, acomponent of light incident vertically to the photomask is required. Onthe other hand, oblique incident exposure cannot provide a dark portiondue to a phase end, even if the phase boundary is generated, andconsequently the contrast enhancement effect cannot be obtained. This isthe reason why the contrast enhancement effect cannot be obtained whenoblique incident exposure is performed with the half-tone phase-shiftingmask. In other words, in order to obtain the contrast enhancement effectwith the half-tone phase-shifting mask, it is necessary to performexposure using a small light source having a low coherence degree.

[0100] As described above, in forming contact patterns, although thelight intensity distribution with the half-tone phase-shifting mask issimilar to that with the outline enhancement mask, the outlineenhancement method can provide a higher contrast to a transferred imageof light, which is necessary for forming small isolated space patterns,even with oblique incident exposure, because of the difference in theprinciple for formation of a dark portion (the phase boundary is notgenerated in the amplitude intensity distribution of the lighttransmitted through the outline enhancement mask (see FIG. 1F).

[0101]FIG. 2A is a plan view of a half-tone phase-shifting mask in whichan opening corresponding to a contact pattern is surrounded by a phaseshifter. FIG. 2B shows calculation results of the light intensitydistribution corresponding to line AA′ when exposure is performed with asmall light source having a small coherence degree σ=0.4 with respect tothe half-tone phase-shifting mask shown in FIG. 2A. FIG. 2C showscalculation results of the light intensity distribution corresponding toline AA′ when exposure is performed with annular illumination, which isone type of oblique incident exposure, with respect to the half-tonephase-shifting mask shown in FIG. 2A. In this case, what is called ⅔annular illumination having an outer diameter σ of 0.75 and an innerdiameter σ of 0.5 is used as the annular illumination. For the exposureconditions, the light source wavelength λ is 193 nm (ArF light source)and the numerical aperture NA is 0.6. The contact size is 180 nm square,and the transmittance of the phase shifter is 6%. In the followingdescription, the light intensity is shown by a relative light intensitywhen taking the light intensity of exposure light as 1, unless otherwisespecified.

[0102] As shown in FIGS. 2B and 2C, when the half-tone phase-shiftingmask is used, a dark portion due to a phase end is formed in the lightintensity distribution from exposure with a small light source and animage having a high contrast can be formed. On the other hand, in thelight intensity distribution from oblique incident exposure, a darkportion due to a phase end is not formed, and therefore an image havinga very poor contrast is formed.

[0103]FIG. 2D is a plan view of an edge enhancement phase-shifting maskin which an opening corresponding to a contact pattern and a phaseshifter positioned in an area surrounding the opening are surrounded bya chromium film serving as a complete light-shielding portion. FIG. 2Eshows calculation results of the light intensity distributioncorresponding to line AA′ when exposure is performed with a small lightsource having a small coherence degree σ=0.4 with respect to the edgeenhancement phase-shifting mask shown in FIG. 2D. FIG. 2F showscalculation results of the light intensity distribution corresponding toline AA′ when exposure is performed with annular illumination withrespect to the edge enhancement phase-shifting mask shown in FIG. 2E.Herein, similarly to the half-tone phase-shifting mask, the “edgeenhancement phase-shifting mask” is a mask that can realize imageenhancement by forming a dark portion due to a phase end between anopening and a phase shifter. The type of annular illumination, theexposure conditions and the transmission of the phase shifter are thesame as those in the case of the half-tone phase-shifting mask shown inFIGS. 2A to 2C. The contact size is 220 nm square, and the width of thephase shifter is 80 nm.

[0104] As shown in FIGS. 2E and 2F, when the edge enhancementphase-shifting mask is used, similarly to the case of the half-tonephase-shifting mask, a dark portion due to a phase end is formed in thelight intensity distribution from exposure with a small light source,and an image having a high contrast can be formed. On the other hand, inthe light intensity distribution from oblique incident exposure, a darkportion due to a phase end is not formed, and therefore an image havinga very poor contrast is formed.

[0105] Next, in the outline enhancement method, before showing in detailthat oblique incident exposure components can provide high contrast, thefact that the structure of the outline enhancement mask as shown in FIG.1E cannot provide the outline enhancement effect when the width of thephase shifter becomes too large will be described.

[0106]FIG. 3A is a plan view of an outline enhancement mask in which anopening corresponding to a contact pattern and a phase shifter having asmall width positioned in an area surrounding the opening are surroundedby a semi-light shielding portion having a transmittance of 6% or moreand 15% or less with respect to exposure light. FIG. 3B showscalculation results of the light intensity distribution corresponding toline AA′ when exposure is performed with a small light source having asmall coherence degree σ=0.4 with respect to the outline enhancementmask shown in FIG. 3A. FIG. 3C shows calculation results of the lightintensity distribution corresponding to line AA′ when exposure isperformed with annular illumination with respect to the outlineenhancement mask shown in FIG. 3A.

[0107]FIG. 3D is a plan view of an outline enhancement mask in which anopening corresponding to a contact pattern and a phase shifter having alarge width positioned in an area surrounding the opening are surroundedby a semi-light shielding portion having a transmittance of 6% or moreand 15% or less with respect to exposure light. FIG. 3E showscalculation results of the light intensity distribution corresponding toline AA′ when exposure is performed with a small light source having asmall coherence degree σ=0.4 with respect to the outline enhancementmask shown in FIG. 3D. FIG. 3F shows calculation results of the lightintensity distribution corresponding to line AA′ when exposure isperformed with annular illumination with respect to the outlineenhancement mask shown in FIG. 3D.

[0108] In this case, it is assumed that the width of the phase shifterin the outline enhancement mask shown in FIG. 3D is set to be too largeto satisfy the principle of the outline enhancement method. Morespecifically, the sizes of the openings shown in FIGS. 3A and 3D areboth 220 nm square, and the width of the phase shifter shown in FIG. 3Ais 60 nm and the width of the phase shifter shown in FIG. 3D is 150 nm.The types of the annular illumination and the exposure conditions arethe same as those in the case of the half-tone phase-shifting mask shownin FIGS. 2A to 2C.

[0109] As shown in FIGS. 3B and 3C, when the outline enhancement maskshown in FIG. 3A that satisfies the principle of the outline enhancementmethod is used, a dark portion due to a non-transparent function of thephase shifter appears regardless of the type of the light source and thecontrast in the light intensity distribution is higher in the annularillumination.

[0110] On the other hand, when the outline enhancement mask shown inFIG. 3D with an excessively large phase shifter is used, the lighttransmitted through the phase shifter is too strong, so that anamplitude intensity distribution having an opposite phase is formed. Inthis situation, the same principle as in the case of the half-tonephase-shifting mask or the edge enhancement phase-shifting mask acts. Inother words, as shown in FIGS. 3E and 3F, a dark portion due to a phaseend is formed in the light intensity distribution obtained by exposurewith a small light source and the contrast enhancement effect isprovided, whereas no dark portion due to a phase end is formed in thelight intensity distribution obtained by oblique incident exposure, sothat an image having very poor contrast is formed.

[0111] In other words, in order to realize the outline enhancementmethod, in the mask structure, it is necessary that not only the phaseshifter is disposed in the periphery of the opening surrounded by thesemi-light shielding portion, but also that the light transmittedthrough the phase shifter is limited. According to the mechanism of theprinciple, the latter means that the light transmitted through the phaseshifter has an intensity that at least can cancel the lights transmittedthrough the semi-light shielding portion and the opening, and theintensity distribution having an opposite phase with a predeterminedsize or more is not formed in its amplitude intensity distribution.

[0112] In order to actually limit the light transmitted through thephase shifter, a condition (more specifically the upper limit) can beimposed on the width of the phase shifter, depending on thetransmittance of the phase shifter. Hereinafter, the condition will bedescribed with reference to the results of observing conditions underwhich the light from the periphery of the phase shifter is cancelled bythe light transmitted through the phase shifter (see FIGS. 4A and 4B).

[0113] As shown in FIG. 4A, in exposure with a photomask (phase shiftermask) in which a phase shifter having a transmittance T and a line widthL is provided on a transparent substrate is used, the light intensitygenerated in a position corresponding to the center of the phase shifterin an exposed material is expressed as Ih (L, T). In exposure with aphotomask (light-shielding mask) in which the phase shifter of thephase-shifting mask is replaced by a complete light-shielding portion isused, the light intensity generated in a position corresponding to thecenter of the complete light-shielding portion in an exposed material isexpressed as Ic (L). In exposure with a photomask (light-transmittingmask) in which the phase shifter of the phase-shifting mask is replacedby an opening (light-transmitting portion) and the light-transmittingportion of the phase-shifting mask is replaced by a completelight-shielding portion is used, the light intensity generated in aposition corresponding to the center of the opening in an exposedmaterial is expressed as Io (L). FIG. 4B is a graph showing thesimulation results of the light intensity Ih (L, T) when thetransmittance T and the line width L of the phase shifter are varied inexposure with the phase-shifting mask shown in FIG. 4A, represented bycontour lines of the light intensity with the transmittance T and theline width L in the vertical axis and the horizontal axis, respectively.In this graph, a graph indicating the relationship of T=Ic (L)/Io (L) issuperimposed. The simulation conditions are such that the wavelength ofthe exposure light λ=0.193 μm (ArF light source), the numerical apertureNA of the projection optical system of the exposure apparatus=0.6, andthe coherence degree σ of the exposure light source=0.8 (regular lightsource).

[0114] As shown in FIG. 4B, the condition under which the lightintensity Ih (L, T) becomes smallest can be expressed by a relationshipT=Ic (L)/Io (L). This physically represents a relationship in which T×Io(L) indicating the light intensity of the light transmitted through thephase shifter is in equilibrium with Ic (L) indicating the lightintensity of the light transmitted outside the phase shifter. Therefore,the width L of the phase shifter that provides an amplitude intensity ofan opposite phase in the amplitude intensity distribution because ofexcessive light transmitted through the phase shifter is a width L thatallows T×Io (L) to be larger than Ic (L).

[0115] It is empirically obtained from various simulation results thatthe width L that allows the light transmitted through the phase shifterhaving a transmittance of 1 to be in equilibrium with the lighttransmitted outside the phase shifter is about 0.3×λ (light sourcewavelength)/NA (numerical aperture) (about 100 nm in the case of FIG.4B), although this may depend on the type of the light source.Furthermore, as seen from FIG. 4B, in order to prevent too much lightfrom being transmitted through the phase shifter having a transmittanceof 6% (0.06) or more, the width L should be not more than twice thewidth of the phase shifter having a transmittance of 100% (1.0). That isto say, in order to prevent too much light from being transmittedthrough the phase shifter having a transmittance of 6% or more, theupper limit of the width L of the phase shifter should be not more than0.6×λ/NA.

[0116] If the above-described findings are applied to the outlineenhancement mask, the upper limit of the width L of the phase shifter inthe outline enhancement mask can be considered to be a half of the upperlimit in the above findings because the light transmitted outside thephase shifter in the outline enhancement mask to be taken intoconsideration is significantly only light on one side rather than bothsides of the phase shifter. Therefore, the upper limit of the width L ofthe phase shifter in the outline enhancement mask is not more than0.3×λ/NA when the transmittance of the phase shifter is 6% or more.However, this is not a sufficient condition, and the upper limit of thewidth L of the phase should be smaller than 0.3×λ/NA, depending on howhigh the transmittance of the phase shifter is. That is to say, when thetransmittance of the phase shifter is as high as 100% or 50% or more,the width L of the phase shifter should be 0.2×λ/NA or less, preferably0.15×λ/NA or less. When forming fine hole patterns, in order to obtainthe effect of enhancing the profile of the light intensity distributionby interference between the light transmitted though the phase shifterand the light transmitted through the light-transmitting portioncorresponding to a hole pattern, it is preferable to arrange the phaseshifter in a region with a distance from the center of thelight-transmitting portion, that is, the hole of 0.5×λ/NA or less.Therefore, when the width L of the phase shifter is 0.3×λ/NA or less, itis preferable in forming hole patterns that the phase shiftersurrounding the light-transmitting portion is present in a region with adistance from the center of the light-transmitting portion correspondingto the hole pattern of 0.5×λ/NA or more and 0.8×λ/NA or less.

[0117] In this specification, unless otherwise specified, various masksizes such as the width of a phase shifter are shown by the sizes on anexposed material. The actual mask size can be obtained easily bymultiplying the sizes on an exposed material by the reduction ratio M ofa reduction projection optical system of an exposure apparatus.

[0118] Next, the image enhancement that can be realized with obliqueincident exposure in the outline enhancement method will be described indetail, based on a change in the contrast of the light intensitydistribution when exposure is performed from various light sourcepositions with respect to the outline enhancement mask.

[0119]FIG. 5A is a plan view of the outline enhancement mask. In thiscase, the transmittance of the semi-light-shielding portion is 7.5%, andthe transmittance of the phase shifter and the opening is 100%. The sizeof the opening is 200 nm square, and the width of the phase shifter is50 nm.

[0120]FIG. 5C shows the results obtained by calculating the lightintensity distribution corresponding to line AA′ of FIG. 5A whenexposure is performed from a point light source in various positionsnormalized with the numerical aperture NA with respect to the outlineenhancement mask shown in FIG. 5A with optical simulations, reading thelight intensity Io in a position corresponding to the center of theopening in the calculation results (e.g., the light intensitydistribution shown in FIG. 5B) and plotting the light intensity Ioagainst each light source position. The results shown in this plot arefrom the optical calculations that are performed assuming that the lightsource wavelength λ is 193 nm (ArF light source) and the numericalaperture NA is 0.6. In the following description, unless otherwisespecified, in the optical simulations, a calculation is performed underthe conditions that the light source wavelength λ is 193 nm (ArF lightsource) and the numerical aperture NA is 0.6.

[0121] As shown in FIG. 5C, the light intensity Io in the center of theopening is larger, as exposure is performed with a point light source ina light position on the outer side (a light source position more apartfrom the origin in FIG. 5C). That is to say, the plot shows that asexposure is performed with a light source having a larger obliqueincident component, the contrast is larger. This will be described morespecifically with reference to the drawings. FIGS. 5D, 5E, and 5F aregraphs obtained by plotting the light intensity distributioncorresponding to line AA′ of FIG. 5A in sample points P1, P2 and P3 ofthe point light sources shown in FIG. 5C, respectively. As shown inFIGS. 5D, 5E, and 5F, as the position of the point light source is onthe outer side, in other words, as the light source is in the positionthat provides larger oblique incident light, an image of a highercontrast is formed.

[0122] Next, for comparison, a change in the contrast of the lightintensity distribution when exposure is performed from various lightsource positions with respect to the half-tone phase-shifting mask willbe described. FIG. 6A is a plan view of the half-tone phase-shiftingmask. In this case, the transmittance of the phase shifter is 6%, andthe transmittance of the opening is 100%. The size of the opening (sizeon an exposed wafer) is 180 nm square.

[0123]FIG. 6C shows the results obtained by calculating the lightintensity distribution corresponding to line AA′ of FIG. 6A whenexposure is performed from a point light source in various positionsnormalized with the numerical aperture NA with respect to the half-tonephase-shifting mask shown in FIG. 6A with optical simulations, readingthe light intensity Io in a position corresponding to the center of theopening in the calculation results (e.g., the light intensitydistribution shown in FIG. 6B) and plotting the light intensity Ioagainst each light source position.

[0124] As shown in FIG. 6C, the light intensity Io in the center of theopening is larger, as exposure is performed with a point light source ina light position on the inner side (a light source position closer tothe origin in FIG. 6C). That is to say, the plot shows that as exposureis performed with a light source having a larger vertical incidentcomponent, the contrast is larger. This will be described morespecifically with reference to the drawings. FIGS. 6D, 6E, and 6F aregraphs obtained by plotting the light intensity distributioncorresponding to line AA′ of FIG. 6A in sample points P1, P2 and P3 ofthe point light sources shown in FIG. 6C, respectively. As shown inFIGS. 6D, 6E, and 6F, as the position of the point light source is onthe inner side, in other words, as the light source is in the positionthat provides larger vertical incident light, an image of a highercontrast is formed.

[0125] As seen from the comparison between the results shown in FIGS. 5Ato 5F and the results shown in FIGS. 6A to 6F, the outline enhancementmethod makes it possible to enhance the contrast of the light intensitydistribution obtained by oblique incident exposure in forming smallisolated space patterns such as contact patterns, which cannot berealized by the conventional methods.

[0126] The fact that the contrast is improved by the outline enhancementmask has been described so far. Next, the dependence of the contrast andthe DOF on the transmittance of the semi-light-shielding portion in theoutline enhancement mask will be described below. The followingdescription is based on the results obtained by simulations of variousmargins in pattern formation, using the outline enhancement mask shownin FIG. 7A. FIG. 7B shows the light intensity distribution formed whenexposure is performed with respect to the outline enhancement mask shownin FIG. 7A. In FIG. 7B, values regarding various margins defined whenforming a hole pattern with a width of 100 nm using the outlineenhancement mask shown in FIG. 7A are also shown. More specifically, thecritical intensity Ith is the light intensity that allows a resist filmto be exposed, and the margin is defined with respect to this value. Forexample, if Ip is the peak value of the light intensity distribution,Ip/Ith is proportional to the sensitivity with which a resist mask isexposed, and the higher value is more preferable. If Ib is thebackground intensity of light transmitted through thesemi-light-shielding portion, a higher Ith/Ib means that a reduction inthickness of the resist film hardly occurs at pattern formation, and thehigher value is more preferable. In general, it is preferable that avalue of Ith/Ib is at least 2. With the foregoing in mind, each marginwill be described.

[0127]FIG. 7C shows the calculation results regarding the dependence ofthe DOF on the transmittance of a semi-light-shielding portion inpattern formation using the outline enhancement mask shown in FIG. 7A.Here, the DOF is defined as the width of the focus position in which achange in the size of a finished pattern is within 10%. As shown in FIG.7C, the higher transmittance the semi-light-shielding portion has, themore preferable it is for improvement of the DOF. FIG. 7D shows thecalculation results regarding the peak value Ip with respect to thetransmittance of the semi-light shielding portion in pattern formationusing the outline enhancement mask shown in FIG. 7A. As shown in FIG.7D, the higher transmittance the semi-light-shielding portion has, themore preferable it is for improvement of the peak value Ip, that is, thecontrast as well. From the above-described results, in the outlineenhancement mask, the higher transmittance the semi-light-shieldingportion has, the more preferable it is. More specifically, as shown inFIGS. 7C and 7D, the improvement rate of the exposure margin isincreased with an increase of the transmittance from 0% to about 6% andit can be appreciated that it is preferable to use asemi-light-shielding portion having a transmittance of about 6% or more.

[0128]FIG. 7E shows the calculation results regarding the Ith/Ib withrespect to the transmittance of the semi-light shielding portion inpattern formation using the outline enhancement mask shown in FIG. 7A.As shown in FIG. 7E, the higher transmittance the semi-light-shieldingportion has, the lower the value of Ith/Ib is. It is not preferable forimprovement of Ith/Ib that the transmittance is too high. Morespecifically, Ith/Ib is less than 2 when the transmittance of thesemi-light-shielding portion is about 15%. FIG. 7F shows the calculationresults regarding the Ip/Ith with respect to the transmittance of thesemi-light shielding portion in pattern formation using the outlineenhancement mask shown in FIG. 7A. As shown in FIG. 7F, the Ip/Ith has apeak at a transmittance of about 15% of the semi-light-shieldingportion.

[0129] As described above, in the outline enhancement mask, the DOF andthe contrast are improved more, as the transmittance of thesemi-light-shielding portion is higher, and this effect is moresignificant when the transmittance of the semi-light-shielding portionexceeds 6%. On the other hand, to prevent a reduction in thickness ofthe resist film during pattern formation or to optimize the resistsensitivity, it is preferable that the maximum of the transmittance ofthe semi-light-shielding portion is about 15%. Therefore, the optimalvalue of the transmittance of the semi-light-shielding portion in theoutline enhancement mask is 6% or more and 15% or less. That is to say,the semi-light-shielding portion transmits exposure light partially toan extent that the resist is not exposed. In other words, thesemi-light-shielding portion transmits a part of the total amount ofexposure light. Such a semi-light-shielding portion can be formed ofoxides such as ZrSiO, CrAlO, TaSiO, MoSiO or TiSiO.

[0130]FIGS. 8A to 8F are plan views showing variations of a lightshielding mask patterns constituted by a semi-light shielding portionand a phase shifter in the outline enhancement mask provided with anopening corresponding to a contact pattern.

[0131] An outline enhancement mask 1 a shown in FIG. 8A has the samestructure of that of the outline enhancement mask shown in FIG. 1E. Thatis, the outline enhancement mask 1 a is a photomask using a transparentsubstrate 2 a and includes a semi-light-shielding portion 3 a having atransmittance that allows a part of exposure light to be transmitted, anopening 4 a surrounded by the semi-light-shielding portion 3 a andcorresponding to an isolated contact pattern, and a ring-shaped phaseshifter 5 a positioned around the opening 4 a.

[0132] The outline enhancement mask 1 b shown in FIG. 8B is a photomaskusing a transparent substrate 2 b and includes a semi-light-shieldingportion 3 b having a transmittance that allows a part of exposure lightto be transmitted, an opening 4 b surrounded by the semi-light-shieldingportion 3 b and corresponding to an isolated contact pattern, and aphase shifter 5 b constituted by four rectangular phase shifter portionsthat have a side having the same length of each side of the opening 4 band are in contact with the respective sides of the opening 4 b. Thisoutline enhancement mask 1 b has substantially the same characteristicsas those of the outline enhancement mask 1 a in isolated patternformation.

[0133] The outline enhancement mask 1 c shown in FIG. 8C is a photomaskusing a transparent substrate 2 c and includes a semi-light-shieldingportion 3 c having a transmittance that allows a part of exposure lightto be transmitted, an opening 4 c surrounded by the semi-light-shieldingportion 3 c and corresponding to an isolated contact pattern, and aphase shifter 5 c constituted by four rectangular phase shifter portionsthat have a side having a length smaller than each side of the opening 4c and are in contact with the respective sides of the opening 4 c. Thecenter of each phase shifter portion of the phase shifter 5 c is alignedwith the center of the respective side of the opening 4 c. In thisoutline enhancement mask Ic, the size of the resist pattern to be formedafter exposure can be adjusted by changing the length of each phaseshifter portion of the phase shifter 5 c with the width (size) of theopening 4 c unchanged. For example, as the length of each phase shifterportion of the phase shifter 5 c is smaller, the size of the resistpattern becomes larger. In this case, the lower limit within which thelength of each phase shifter portion of the phase shifter 5 c can bechanged without losing the function of outline enhancement is limited toabout a half of the wavelength of the light source (exposure light). Onthe other hand, since the pattern size is changed only to an extent ofabout a half of the change amount of the mask size, adjusting the lengthof the phase shifter portion is an excellent approach to adjust thepattern size.

[0134] The outline enhancement mask 1 d shown in FIG. 8D is a photomaskusing a transparent substrate 2 d and includes a semi-light-shieldingportion 3 d having a transmittance that allows a part of exposure lightto be transmitted, an opening 4 d surrounded by the semi-light-shieldingportion 3 d and corresponding to an isolated contact pattern, and aring-shaped phase shifter 5 d positioned apart from the boundary of thesemi-light-shielding portion 3 d and the opening 4 d by a predetermineddistance on the side of the semi-light-shielding portion 3 d. That is tosay, a ring-shaped semi-light-shielding portion 3 d is present betweenthe phase shifter 5 d and the opening 4 d.

[0135] The outline enhancement mask le shown in FIG. 8E is a photomaskusing a transparent substrate 2 c and includes a semi-light-shieldingportion 3 c having a transmittance that allows a part of exposure lightto be transmitted, an opening 4 e surrounded by the semi-light-shieldingportion 3 e and corresponding to an isolated contact pattern, and aphase shifter 5 e positioned apart from the boundary of thesemi-light-shielding portion 3 c and the opening 4 e by a predetermineddistance on the side of the semi-light-shielding portion 3 e. The phaseshifter 5 e is constituted by four phase shifter portions, each of whichis a rectangular shape having a length larger than each side of theopening 4 e and whose corner is in contact with the corners of theadjacent portions on the diagonal line of the opening 4 e. In this case,a ring-shaped semi-light-shielding portion 3 e is present between thephase shifter 5 e and the opening 4 e. In this outline enhancement maskle, the size of the resist pattern to be formed after exposure can beadjusted by changing only the width (size) of the opening 4 e with thesize and the arrangement of the phase shifter 5 e with unchanged. Forexample, as the width of the opening 4 e is increased, the size of theresist pattern is increased. According to this approach of adjusting thepattern size by changing only the width of the opening, MEEF (Mask ErrorEnhancement Factor: the ratio of the change amount of the pattern sizewith respect to the change amount of the mask size) is reduced to abouta half of that obtained by an approach of scaling both the opening andthe phase shifter at the same time to adjust the pattern size.

[0136] The outline enhancement mask 1 f shown in FIG. 8F is a photomaskusing a transparent substrate 2 f and includes a semi-light-shieldingportion 3 f having a transmittance that allows a part of exposure lightto be transmitted, an opening 4 f surrounded by the semi-light-shieldingportion 3 f and corresponding to an isolated contact pattern, and aphase shifter 5 f positioned apart from the boundary of thesemi-light-shielding portion 3 f and the opening 4 f by a predetermineddistance on the side of the semi-light-shielding portion 3 f. The phaseshifter 5 f is constituted by four phase shifter portions, each of whichis a rectangular shape having the same length as that of each side ofthe opening 4 f and whose side is opposed to the corresponding side ofthe opening 4 f. In this case, the length of each phase shifter portionof the phase shifter 5 f may be larger or smaller than that of the sideof the opening 4 f. According to this outline enhancement mask 1 f, thesize of the resist pattern can be adjusted as in the case of the outlineenhancement mask Ic shown in FIG. 8C.

[0137] In the outline enhancement masks shown in FIGS. 8D to 8F, inorder to increase the effect of reducing the MEEF, it is preferable thatthe width of the semi-light-shielding portion between the opening andthe phase shifter is about ⅕ of λ/NA (λ is the wavelength of theexposure light and NA is the numerical aperture). In order to obtain theeffect of improving the DOF, it is preferable that the width of thesemi-light-shielding portion is a size that allows an interferenceeffect of light by the phase shifter to be provided, that is, about{fraction (1/10)} of λ/NA or less. In the outline enhancement masksshown in FIGS. 8A to 8F, a square is used as the shape of the opening.However, a polygon such as an octagon or a circle, or other shapes canbe used. The shape of the phase shifter is not limited to a continuousring shape or a plurality of rectangles. For example, the phase shiftercan be formed by aligning a plurality of square phase shifter portions.

[0138] All the above description has been based on the positive resistprocess in which the portion corresponding to a resist-removed portionin the outline enhancement mask is defined as the opening. However, if aphase shifter having a sufficiently high transmittance can be used, inthe outline enhancement mask used for the above description, the portiondefined as the opening can be replaced by a phase shifter having a hightransmittance, the portion defined as the phase shifter can be replacedby an opening, and the portion defined as the semi-light-shieldingportion can be replaced by a phase shifter having a low transmittance(e.g., a phase shifter of a half-tone phase-shifting mask). In thiscase, the relationship of the relative phase difference between theelements is the same as in the above-described case, so that an outlineenhancement mask having the same effect can be realized.

[0139] First Embodiment

[0140] Hereinafter, a photomask according to a first embodiment of thepresent invention, a method for producing the photomask and a method forforming a pattern using the photomask will be described with referenceto the accompanying drawings. The photomask of the first embodiment is aphotomask of a reduction projection exposure system to realize theabove-described outline enhancement method.

[0141]FIG. 9A shows an example of a desired pattern to be formed withthe photomask of the first embodiment.

[0142] When the reduction ratio of a reduction projection optical systemof an exposure apparatus is M, in a regular photomask, a pattern havinga size M times the size of a desired pattern (in general, having adesigned value on a wafer) is drawn on a substrate (transparentsubstrate) formed of a material having a high transmittance with respectto exposure light, using a material, such as chromium film serving as acomplete light-shielding portion with respect to the exposure light.However, in this specification, for simplification, the presentinvention is described, using the size on a wafer rather than using thesize on the mask, which is a size M times the size on a wafer, unlessotherwise specified. In this embodiment, when describing patternformation, the description is based on the positive resist process,unless otherwise specified. That is to say, the description is based onthe assumption that an exposed portion of the resist film is removed. Onthe other hand, when a negative resist process is assumed to be used,the description is totally the same as in the case of the positiveresist process, except that the exposed portion of the resist filmbecomes a resist pattern. In this embodiment, the transmittance isexpressed by an effective transmittance when the transmittance of thetransparent substrate is taken as 100%, unless otherwise specified.

[0143]FIG. 9B is a plan view of the photomask of the first embodiment,more specifically, a photomask for forming the desired pattern shown inFIG. 9A. As shown in FIG. 9B, openings (light-transmitting portions) areprovided so as to correspond to resist-removed portions in the desiredpattern. Furthermore, a semi-light-shielding portion having a lowtransmittance (about 6 to 15%) that does not allow the resist film to beexposed and transmits exposure light in the same phase as that of theopening is used as the light-shielding mask pattern surrounding theopening, instead of the complete light-shielding portion that completelyshields exposure light. In the first embodiment, the transmittance ofthe semi-light-shielding portion is set to, for example, 7.5%. Phaseshifters (peripheral portions) that transmit exposure light in a phaseopposite to that of the opening are provided in the periphery of theopenings. In this embodiment, the transmittance of the phase shifters isset to a higher value than that of the semi-light-shielding portion, forexample, 20% so that the light transmitted through the phase shifter cancancel the lights transmitted through the openings and thesemi-light-shielding portions effectively, according to the principle ofthe outline enhancement method.

[0144] In the first embodiment, for example, as shown in FIG. 8B, thephase shifters are arranged in such a manner that the sides of the phaseshifters are in contact with the corresponding sides of the rectangularopening in a region having a predetermine size or less from each side ofthe rectangular opening.

[0145]FIG. 9C is a cross-sectional view taken along line AA′ in FIG. 9B,that is a cross-sectional view of the photomask of the first embodiment.As shown in FIG. 9C, the surface of the transparent substrate 10 in theopening (light-transmitting portion) formation region is exposed. Alower phase shift film 11 that transmits exposure light with a phasedifference (opposite phase) of 180 degrees (more specifically(150+360×n) degrees or more and (210+360×n) degrees or less (where n isan integer)) between this film and the opening is formed on thetransparent substrate 10 in the phase shifter (peripheral portion)formation region. The lower phase shift film 11 and an upper phase shiftfilm 12 that transmits exposure light in a phase opposite to that of theopening are laminated sequentially on the transparent substrate 10 inthe semi-light-shielding portion formation region. As the lower phaseshift film 11 and the upper phase shift film 12, an oxide film such asZrSiO, CrAlO, TaSiO, MoSiO or TiSiO can be used. However, it ispreferable that the lower phase shift film 11 and the upper phase shiftfilm 12 are formed of different oxide films each other. Here, the lowerphase shift film 11 is a phase shift film having a transmittance of 20%as a single film. On the other hand, the structure in which the lowerphase shift film 11 and the upper phase shift film 12 are laminated actsas a semi-light-shielding film that has a transmittance of 7.5% andcauses a phase difference (the same phase) of 360 degrees (morespecifically, (−30+360×n) degrees or more and (30+360×n) degrees orless, (where n=an integer)). In other words, the structure in which thelower phase shift film 11 and the upper phase shift film 12 arelaminated acts as a half-tone film in which phase inversion does notoccur. Furthermore, a peripheral portion, that is, a phase shifterhaving a single layered structure of the lower phase shift film 11 isformed between the semi-light-shielding portion and the opening. Asdescribed above, the photomask of this embodiment acts as an outlineenhancement mask. However, as described above, in order to obtaincontrast enhancement by the outline enhancement method, it is necessaryto limit the width of the phase shifter to a predetermined size or less.

[0146] In the above description, as shown in FIG. 10A, it is assumedthat the lower phase shift film 11 and the upper phase shift film 12 areeach a single layered film. In this case, the optical constant of eachphase shift film is determined by its material, so that the thickness ofeach phase shift film is determined by the amount of the phase shift. Onthe other hand, the transmittance depends on not only the opticalconstant, but also the film thickness, so that for the material of thephase shift film, a material having an appropriate optical constant,more specifically, a material that can achieve exactly a predeterminedtransmittance with a thickness that can transmit exposure light in aphase opposite to that of the opening is not necessarily present.Therefore, in the first embodiment, as shown in FIG. 10B, it ispreferable that the lower phase shift film 11 has a first transmittanceadjusting film 11A and a first phase adjusting film 11B on the firsttransmittance adjusting film 11A, and the upper phase shift film 12 hasa second transmittance adjusting film 12A and a second phase adjustingfilm 12B on the second transmittance adjusting film 12A in order toachieve an arbitrary transmittance in each phase shift film. The firsttransmittance adjusting film 11A and the second transmittance adjustingfilm 12A transmit exposure light in the same phase as that of theopening and have a relatively low transmittance with respect to exposurelight. On the other hand, the first phase adjusting film 11B and thesecond phase adjusting film 12B transmit exposure light in a phaseopposite to that of the opening and have a relatively high transmittancewith respect to exposure light. As the first transmittance adjustingfilm 11A and the second transmittance adjusting film 12A, a thin film(having a thickness of 30 nm or less) made of a metal such as Zr, Cr,Ta, Mo or Ti or a thin film (having a thickness of 30 nm or less) madeof a metal alloy such as a Ta—Cr alloy, a Zr—Si alloy, a Mo—Si alloy ora Ti—Si alloy can be used. As the first phase adjusting film 11B and thesecond phase adjusting film 12B, an oxide film such as SiO₂ film can beused.

[0147] In FIG. 10B, an example in which both the lower phase shift film11 and the upper phase shift film 12 have a two layered structure isillustrated, but one of the lower phase shift film 11 and the upperphase shift film 12 may have a two layered structure, and the other mayhave a single layered structure.

[0148] In this specification, a transmittance adjusting film refers to afilm that has relatively a low transmittance per unit thickness withrespect to exposure light and can set the transmittance with respect toexposure light to a desired value by adjusting the thickness withoutaffecting the phase change with respect to the exposure light. A phaseadjusting film refers to a film that has relatively a high transmittanceper unit thickness with respect to exposure light and can set the phasedifference with respect to exposure light between this film and thetransparent substrate (opening) to a desired value by adjusting thethickness without affecting the transmittance change with respect to theexposure light.

[0149] Next, a method for forming a pattern using the photomask of thefirst embodiment will be described. As described with reference to theprinciple of the outline enhancement method when transferring a maskpattern in a reduced size with an exposure apparatus, it is preferableto use an oblique incident exposure light source in order to form animage having a high contrast with the outline enhancement mask. Herein,“oblique incident exposure” refers to light sources shown in FIGS. 11Bto 11D in which vertical incident components are removed, as opposed toa regular exposure light source as shown in FIG. 11A. Representativeoblique incident exposure light sources are an annular exposure lightsource shown in FIG. 11B and a quadrupole exposure light source shown inFIG. 11C. Although it depends slightly on a desired pattern, in general,quadrupole exposure light sources are more advantageous in enhancementof the contrast and enlargement of the DOF than annular exposure lightsources. However, quadrupole exposure light sources have such sideeffects that a pattern shape is distorted from the mask shape, so thatin such a case, it is preferable to use an annular-quadrupole mixed typeexposure light source as shown in FIG. 11D. The annular-quadrupole mixedtype exposure light source is characterized by having a feature of aquadrupole light source that the center of the light source and thelight sources on the XY axis are removed when assuming the XY coordinatewith the center of the light source (center of a regular exposure lightsource) as the origin, and having a feature of an annular light sourcethat a circle is used as the contour of the light source.

[0150]FIGS. 12A to 12D are cross-sectional views showing the processesof a method forming patterns with the photomask of the first embodiment.

[0151] First, as shown in FIG. 12A, after a film 101 to be processedsuch as a metal film or an insulating film is formed on a substrate 100,as shown in FIG. 12B, a positive resist film 102 is formed on the film101 to be processed.

[0152] Next, as shown in FIG. 12C, the photomask of the first embodimentincluding a semi-light-shielding portion made of a multilayeredstructure of the lower phase shift film 11 and the upper phase shiftfilm 12 and a phase shifter made of a single layered structure of thelower phase shift film 11 is irradiated with exposure light 103 with anoblique incident exposure light source to expose the resist film 102with transmitted light 104 transmitted through the photomask. In thiscase, a semi-light-shielding portion having a low transmittance is usedas the mask pattern, so that the entire resist film 102 is exposed withweak energy. However, as shown in FIG. 12C, only a latent image portion102 a of the resist film 102 corresponding to the light-transmittingportion (opening) in the photomask is irradiated with the exposureenergy that is sufficient to dissolve the resist film 102 in adeveloping process.

[0153] Next, the latent image portion 102 a is removed by performingdevelopment with respect to the resist film 102, so that as shown inFIG. 12D, a resist pattern 105 is formed. In this case, in the exposureprocess shown in FIG. 12C, light in the periphery of the opening iscanceled, so that a portion corresponding to the phase shifter(peripheral portion) in the resist film 102 is substantially notirradiated with exposure energy. Therefore, the contrast in the lightintensity distribution between the light transmitted through the openingand the light transmitted through the peripheral portion, in otherwords, the contrast in the light intensity distribution between thelight with which the latent image portion 102 a is irradiated and thelight with which the periphery of the latent portion 102 a is irradiatedcan be enhanced. Therefore, the energy distribution in the latentportion 102 a is changed sharply, so that a resist pattern 105 having asharp shape can be formed.

[0154] Next, a method for producing a photomask of the first embodimentwill be described with reference to the drawings.

[0155]FIGS. 13A to 13E are cross-sectional views showing the processesof a method producing the photomask of the first embodiment. FIG. 13F isa plan view corresponding to the cross-sectional view of FIG. 13C, andFIG. 13G is a plan view corresponding to the cross-sectional view ofFIG. 13E.

[0156] First, as shown in FIG. 13A, a lower phase shift film 11 made of,for example, TaSiO and an upper phase shift film 12 made of, forexample, MoSiO are formed sequentially on a transparent substrate 10made of a material having light-transmitting properties with respect toexposure light, such as quartz. As the lower phase shift film 11 and theupper phase shift film 12, an oxide film such as ZrSiO, CrAlO, TaSiO,MoSiO or TiSiO can be used. However, it is preferable that the lowerphase shift film 11 and the upper phase shift film 12 are made ofdifferent oxides each other so that the upper phase shift film 12 can beremoved selectively from the lower phase shift film 11. Furthermore, thelower phase shift film 11 and the upper phase shift film 12 eachgenerate a phase difference of (150+360×n) degrees or more and(210+360×n) degrees or less (where n an integer) with respect toexposure light between these films and the light-transmitting portion(opening) in the transparent substrate 10. In this embodiment, at leastone of the lower phase shift film 11 and the upper phase shift film 12may have a two layered structure of a transmittance adjusting film and aphase adjusting film as described above.

[0157] Next, as shown in FIG. 13B, a first resist pattern 13 that coversthe semi-light-shielding portion formation region is formed on thetransparent substrate 10. That is, a first resist pattern 13 having aremoved portion in each of the opening (light-transmitting portion)formation region and the phase shifter (peripheral portion) formationregion is formed on the transparent substrate 10. Thereafter, the upperphase shift film 12 is etched with the first resist pattern 13 as a maskto pattern the upper phase shift film 12. Then, the first resist pattern13 is removed. Thus, as shown in FIGS. 13C and 13F, the portionscorresponding to the opening formation region and the phase shifterformation region in the upper phase shift film 12 are removed.

[0158] Next, as shown in FIG. 13D, a second resist pattern 14 thatcovers the semi-light-shielding portion formation region and the phaseshifter formation region is formed on the transparent substrate 10. Thatis, a second resist pattern 14 having a removed portion in the openingformation region is formed. Thereafter, the lower phase shift film 11 isetched with the second resist pattern 14 as a mask to pattern the lowerphase shift film 11. Then, the second resist pattern 14 is removed.Thus, as shown in FIGS. 13E and 13G, the portion corresponding to theopening formation region in the lower phase shift film 11 is removed,and thus the photomask of the first embodiment is completed. That is tosay, the photomask of the first embodiment having the plane structure ofthe outline enhancement mask can be easily formed by, as a mask blank,preparing a transparent substrate in which two half-tone phase shiftfilms are deposited, and then performing selective etching with respectto the lower and upper phase shift films sequentially.

[0159] As described above, according to the first embodiment, the lowerphase shift film 11 and the upper phase shift film 12 that transmitexposure light with a phase inversion are formed sequentially on thetransparent substrate 10. Then, the portions of upper phase shift film12 in the opening (light-transmitting portion) formation region and thephase shifter (peripheral portion) formation region is removed.Thereafter, the portion of the lower phase shift film 11 in the openingformation region is removed. That is to say, the opening is made of theexposed portion of the transparent substrate 10, and thesemi-light-shielding portion is made of a multilayered structure of thelower phase shift film 11 and the upper phase shift film 12. The phaseshifter is made of a single layered structure of the lower phase shiftfilm 11. The multilayered structure of the lower phase shift film 11 andthe upper phase shift film 12 transmits exposure light in the same phaseas that of the opening. Therefore, the phase shifter that transmitsexposure light in the phase opposite to that of the opening issandwiched by the opening and the semi-light-shielding portion thattransmits exposure light in the same phase as that of the opening. As aresult, the contrast in the light intensity distribution between theopening and the phase shifter can be enhanced by mutual interferencebetween the light transmitted through the opening and the lighttransmitted through the phase shifter. This contrast enhancement effectalso can be obtained when a fine isolated resist-removed portion (i.e.,a fine isolated space pattern corresponding to the light-transmittingportion) is formed with oblique incident exposure, for example, in thepositive resist process. That is to say, it is possible to miniaturizeisolated space patterns and isolated line patterns or dense patterns atthe same time with oblique incident exposure.

[0160] According to the first embodiment, the lower phase shift film 11and the upper phase shift film 12 that are laminated on the transparentsubstrate 10 are etched selectively, so that a mask pattern with anyshape that has the semi-light-shielding portion and the phase shifter(peripheral portion) can be easily realized.

[0161] According to the first embodiment, a phase shifter with any shapecan be formed by processing the upper phase shift film 12 of themultilayered structure of the lower phase shift film 11 and the upperphase shift film 12 constituting the semi-light-shielding portion. Forthis reason, as the pattern layout of the outline enhancement mask, notonly the type shown in FIGS. 9B and 9C, that is, the type shown in FIG.8B, but also all the types shown in FIGS. 8A to 8F, for example, can berealized.

[0162] According to the first embodiment, the transmittance of the phaseshifter can be defined by the single layered structure of the lowerphase shift film 11, and the transmittance of the semi-light-shieldingportion can be defined by the multilayered structure of the lower phaseshift film 11 and the upper phase shift film 12, so that a combinationof the transmittances of the phase shifter and the semi-light-shieldingportion can be set arbitrarily.

[0163] In the first embodiment, it is preferable that the transmittanceof the semi-light-shielding portion (multilayered structure of the lowerphase shift film 11 and the upper phase shift film 12) is 6% or more and15% or less. Thus, the contrast enhancement effect can be obtainedreliably while preventing a reduction in thickness of the resist film inpattern formation.

[0164] In the first embodiment, the description is based on the use ofthe positive resist process, but the negative resist process can beused, instead of the positive resist process. In this case, in eitherone of the processes, as the exposure light source, the i line(wavelength 365 nm), KrF excimer laser light (wavelength 248 nm), ArFexcimer laser light (wavelength 193 nm), or F₂ excimer laser light(wavelength 157 nm) can be used, for example.

[0165] First Variation of the First Embodiment

[0166] Hereinafter, a photomask of a first variation of the firstembodiment and a method for producing the photomask will be describedwith reference to the accompanying drawings.

[0167] The first variation of the first embodiment is different from thefirst embodiment in the following aspects. In the first embodiment, theoutline enhancement mask having a layout in which the phase shifter(peripheral portion) and the opening (light-transmitting portion) areadjacent as shown, for example, in FIGS. 8A to 8C is described. In thefirst variation of the first embodiment, the outline enhancement maskhaving a layout in which the phase shifter and the opening are apart asshown, for example, in FIGS. 8D to 8F is described.

[0168]FIGS. 14A to 14E are cross-sectional views showing the processesof a method producing a photomask of the first variation of the firstembodiment. FIG. 14F is a plan view corresponding to the cross-sectionalview of FIG. 14C, and FIG. 14G is a plan view corresponding to thecross-sectional view of FIG. 14E.

[0169] First, as shown in FIG. 14A, a lower phase shift film 11 and anupper phase shift film 12 are formed sequentially on a transparentsubstrate 10 made of a material having light-transmitting propertieswith respect to exposure light, such as quartz. The lower phase shiftfilm 11 and the upper phase shift film 12 generate a phase difference(opposite phase) of (150+360×n) degrees or more and (210+360×n) degreesor less (where n=an integer) with respect to exposure light betweenthese films and the light-transmitting portion (opening) in thetransparent substrate 10. In this variation, at least one of the lowerphase shift film 11 and the upper phase shift film 12 may have a twolayered structure of a transmittance adjusting film and a phaseadjusting film (see the first embodiment).

[0170] Next, as shown in FIG. 14B, a first resist pattern 13 that coversa semi-light-shielding portion formation region is formed on thetransparent substrate 10. That is, a first resist pattern 13 having aremoved portion in each of an opening (light-transmitting portion)formation region and a phase shifter (peripheral portion) formationregion is formed on the transparent substrate 10. In this variation, theopening formation region and the phase shifter formation region areapart. In other words, the first resist pattern 13 is interposed betweenthe opening formation region and the phase shifter formation region.Thereafter, the upper phase shift film 12 is etched with the firstresist pattern 13 as a mask to pattern the upper phase shift film 12.Then, the first resist pattern 13 is removed. Thus, as shown in FIGS.14C and 14F, the portions corresponding to the opening formation regionand the phase shifter formation region in the upper phase shift film 12are removed.

[0171] Next, as shown in FIG. 14D, a second resist pattern 14 thatcovers the semi-light-shielding portion formation region including thephase shifter formation region and that has a removed portion in theopening formation region is formed on the transparent substrate 10.Thereafter, the lower phase shift film 11 is etched with the secondresist pattern 14 and the patterned upper phase shift film 12 as masksto pattern the lower phase shift film 11. Then, the second resistpattern 14 is removed. Thus, as shown in FIGS. 14E and 14G, the portioncorresponding to the opening formation region in the lower phase shiftfilm 11 is removed, and thus the photomask of the first variation of thefirst embodiment is completed.

[0172] According to the first variation of the first embodiment, thefollowing advantages can be obtained, in addition to those of the firstembodiment. Since the patterned upper phase shift film 12 is used as amask for etching the lower phase shift film 11 in a self-alignmentmanner, photomask process can be performed precisely.

[0173] Second Variation of the First Embodiment

[0174] Hereinafter, a photomask of a second variation of the firstembodiment and a method for producing the photomask will be describedwith reference to the accompanying drawings.

[0175] The second variation of the first embodiment is different fromthe first embodiment in the following aspects. In the first embodiment,the outline enhancement mask having a layout in which the phase shifter(peripheral portion) and the opening (light-transmitting portion) areadjacent as shown, for example, in FIGS. 8A to 8C is described. In thesecond variation of the first embodiment as well as the first variationof the first embodiment, the outline enhancement mask having a layout inwhich the phase shifter and the opening are apart as shown, for example,in FIGS. 8D to 8F is described.

[0176]FIGS. 15A to 15E are cross-sectional views showing the processesof a method producing a photomask of the second variation of the firstembodiment. FIG. 15F is a plan view corresponding to the cross-sectionalview of FIG. 15C, and FIG. 15G is a plan view corresponding to thecross-sectional view of FIG. 15E.

[0177] First, as shown in FIG. 15A, a lower phase shift film 11 and anupper phase shift film 12 are formed sequentially on a transparentsubstrate 10 made of a material having light-transmitting propertieswith respect to exposure light, such as quartz. The lower phase shiftfilm 11 and the upper phase shift film 12 generate a phase difference(opposite phase) of (150+360×n) degrees or more and (210+360×n) degreesor less (where n=an integer) with respect to exposure light betweenthese films and the light-transmitting portion (opening) in thetransparent substrate 10. In this variation, at least one of the lowerphase shift film 11 and the upper phase shift film 12 may have a twolayered structure of a transmittance adjusting film and a phaseadjusting film (see the first embodiment).

[0178] Next, as shown in FIG. 15B, a first resist pattern 13 that coversa semi-light-shielding portion formation region and an opening(light-transmitting portion) formation region is formed on thetransparent substrate 10. That is, a first resist pattern 13 having aremoved portion in a phase shifter (peripheral portion) formation regionis formed on the transparent substrate 10. Thereafter, the upper phaseshift film 12 is etched with the first resist pattern 13 as a mask topattern the upper phase shift film 12. Then, the first resist pattern 13is removed. Thus, as shown in FIGS. 15C and 15F, the portioncorresponding to the phase shifter formation region in the upper phaseshift film 12 is removed.

[0179] Next, as shown in FIG. 15D, a second resist pattern 14 thatcovers the semi-light-shielding portion formation region and the phaseshifter formation region is formed on the transparent substrate 10. Thatis to say, a second resist pattern 14 that has a removed portion in theopening formation region is formed on the transparent substrate 10.Thereafter, the upper phase shift film 12 and the lower phase shift film11 are etched sequentially with the second resist pattern 14 as a maskto pattern each phase shift film. Then, the second resist pattern 14 isremoved. Thus, as shown in FIGS. 15E and 15G, the portions correspondingto the opening formation region in the lower phase shift film 11 and theupper phase shift film 12 are removed, and thus the photomask of thesecond variation of the first embodiment is completed.

[0180] According to the second variation of the first embodiment, thefollowing advantages can be obtained, in addition to those of the firstembodiment. In this variation, the process of removing the portioncorresponding to the phase shifter formation region in the upper phaseshift film 12 (see FIG. 15C) and the process of removing the portioncorresponding to the opening formation region in the upper phase shiftfilm 12 (see FIG. 15E) are performed separately. Therefore, if theopening is apart from the phase shifter with a small distance, in otherwords, if a semi-light-shielding portion having a small width made of amultilayered structure of the lower phase shift film 11 and the upperphase shift film 12 is present between the opening and the phaseshifter, the margin for photomask process is increased.

[0181] In the second variation of the first embodiment, beforeperforming the process of removing the portion corresponding to thephase shifter formation region in the upper phase shift film 12, theprocess of removing the portions corresponding to the opening formationregion in the lower phase shift film 11 and the upper phase shift film12 may be performed.

[0182] Second Embodiment

[0183] Hereinafter, a photomask according to a second embodiment of thepresent invention, a method for producing the photomask and a method forforming a pattern using the photomask will be described with referenceto the accompanying drawings. The photomask of the second embodiment isa photomask of a reduction projection exposure system to realize theabove-described outline enhancement method.

[0184]FIG. 16A shows an example of a desired pattern to be formed withthe photomask of the second embodiment. In this embodiment as well asthe first embodiment, the description is based on the assumption thatthe positive resist process is used. Furthermore, in this embodiment,the transmittance is expressed by an effective transmittance when thetransmittance of the transparent substrate is taken as 100%, unlessotherwise specified.

[0185]FIG. 16B is a plan view of the photomask of the second embodiment,more specifically, a photomask for forming the desired pattern shown inFIG. 16A. As shown in FIG. 16B, openings (light-transmitting portions)are provided so as to correspond to resist-removed portions in thedesired pattern. Furthermore, a semi-light-shielding portion having alow transmittance (about 6 to 15%) that does not allow the resist filmto be exposed and transmits exposure light in the same phase as that ofthe opening is used as the light-shielding mask pattern surrounding theopening, instead of the complete light-shielding portion that completelyshields exposure light. Furthermore, phase shifters (peripheralportions) that transmit exposure light in a phase opposite to that ofthe openings are provided in the periphery of the openings. In thisembodiment, the transmittance of the phase shifter is set to a highervalue than that of the semi-light-shielding portion so that the lighttransmitted through the phase shifters can cancel effectively the lighttransmitted through the openings and the semi-light-shielding portion,according to the principle of the outline enhancement method.

[0186] In the second embodiment, the phase shifters are arranged in sucha manner that the sides of the phase shifters are in contact with thecorresponding sides of the rectangular opening in a region having apredetermine size or less from each side of the rectangular opening, forexample, as shown in FIG. 8B.

[0187]FIG. 16C is a cross-sectional view taken along line AA′ in FIG.16B, that is a cross-sectional view of the photomask of the secondembodiment. As shown in FIG. 16C, the surface of the transparentsubstrate 20 in the opening (light-transmitting portion) formationregion is exposed. A lower phase adjusting film 21 is formed on thetransparent substrate 20 in the phase shifter (peripheral portion)formation region. The lower phase adjusting film 21, a transmittanceadjusting film 22 and an upper phase adjusting film 23 are formedsequentially on the transparent substrate 20 in the semi-light-shieldingportion formation region. The lower phase adjusting film 21 and theupper phase adjusting film 23 constitute a phase shift film thattransmits exposure light with a phase difference (opposite phase) of 180degrees (more specifically (150+360×n) degrees or more and (210+360×n)degrees or less (where n is an integer)) between this film and theopening. The transmittance adjusting film 22 has a lower transmittancethan those of the lower phase adjusting film 21 and the upper phaseadjusting film 23. As the lower phase shift film 21 and the upper phaseadjusting film 23, an oxide film such as SiO₂ film can be used. As thetransmittance adjusting film 22, a thin film (having a thickness of 30nm or less) made of a metal such as Zr, Cr, Ta, Mo or Ti or a thin film(having a thickness of 30 nm or less) made of a metal alloy such as aTa—Cr alloy, a Zr—Si alloy, a Mo—Si alloy or a Ti—Si alloy can be used.The lower phase adjusting film 21 is a phase shift film that has a veryhigh transmittance as a single film and transmits exposure light in aphase opposite to that of the opening (transparent substrate 20). Thetransmittance of the transmittance adjusting film 22 is set such thatthe multilayered structure of the lower phase adjusting film 21, thetransmittance adjusting film 22 and the upper phase adjusting film 23has a predetermined transmittance (low transmittance that does not allowthe resist film to be exposed) with respect to exposure light. Moreover,the multilayered structure of the lower phase adjusting film 21, thetransmittance adjusting film 22 and the upper phase adjusting film 23transmits exposure light in the same phase (more specifically, the phasedifference of (−30+360×n) degrees or more and (30+360×n) degrees orless, (where n=an integer)) between this structure and the opening(transparent substrate 20). That is to say, the multilayered structureof the lower phase adjusting film 21, the transmittance adjusting film22 and the upper phase adjusting film 23 constitute asemi-light-shielding portion that transmits exposure light in the samephase as that of the opening and has a predetermined transmittance withrespect to exposure light. Thus, the peripheral portion, that is, aphase shifter, having a single layered structure of the lower phaseadjusting film 21 is formed between the semi-light-shielding portion andthe opening, and thus an outline enhancement mask is realized. However,in order to enhance the contrast by the outline enhancement method, itis necessary to limit the width of the phase shifter to a predeterminedsize.

[0188] A method for producing the photomask of the second embodiment isas follows. The lower phase adjusting film 21, the transmittanceadjusting film 22 and the upper phase adjusting film 23 are formedsequentially on the transparent substrate 20 made of a material havinglight-transmitting properties with respect to exposure light (e.g.,quartz). Thereafter, the upper phase adjusting film 23, thetransmittance adjusting film 22 and the lower phase adjusting film 21are selectively etched sequentially. More specifically, if the lowerphase adjusting film 21 is regarded as a lower phase shift film and thetransmittance adjusting film 22 and the upper phase adjusting film 23are regarded as an upper phase shift film, the method for producing thephotomask of the first embodiment shown in FIGS. 13 to 15 can be used asit is to produce the photomask of the second embodiment.

[0189] Next, a method for forming a pattern using the photomask of thesecond embodiment will be described. In this case, as described withreference to the principle of the outline enhancement method whentransferring a mask pattern in a reduced size with an exposureapparatus, it is preferable to use an oblique incident exposure lightsource as shown in FIGS. 11B to 11D in order to form an image having ahigh contrast with the outline enhancement mask.

[0190]FIGS. 17A to 17D are cross-sectional views showing the processesof a method forming a pattern with the photomask of the secondembodiment.

[0191] First, as shown in FIG. 17A, after a film 201 to be processedsuch as a metal film or an insulating film is formed on a substrate 200,as shown in FIG. 17B, a positive resist film 202 is formed on the film201 to be processed.

[0192] Next, as shown in FIG. 17C, the photomask of the secondembodiment including the semi-light-shielding portion made of themultilayered structure of the lower phase adjusting film 21, thetransmittance adjusting film 22 and the upper phase adjusting film 23,and a phase shifter made of the single layered structure of the lowerphase adjusting film 21 is irradiated with exposure light 203 with anoblique incident exposure light source to expose the resist film 202with transmitted light 204 transmitted through the photomask. In thiscase, the semi-light-shielding portion having a low transmittance isused as the mask pattern, so that the entire resist film 202 is exposedwith weak energy. However, as shown in FIG. 17C, only a latent imageportion 202 a of the resist film 202 corresponding to thelight-transmitting portion (opening) in the photomask is irradiated withexposure energy that is sufficient to dissolve the resist film 202 in adeveloping process.

[0193] Next, the latent image portion 202 a is removed by performingdevelopment with respect to the resist film 202, so that as shown inFIG. 17D, a resist pattern 205 is formed. In this case, in the exposureprocess shown in FIG. 17C, light in the periphery of the opening iscanceled, so that a portion corresponding to the phase shifter(peripheral portion) in the resist film 202 is substantially notirradiated with exposure energy. Therefore, the contrast in the lightintensity distribution between the light transmitted through the openingand the light transmitted through the peripheral portion, in otherwords, the contrast in the light intensity distribution between thelight with which the latent image portion 202 a is irradiated and thelight with which the periphery of the latent portion 202 a is irradiatedcan be enhanced. Therefore, the energy distribution in the latentportion 202 a is changed sharply, so that a resist pattern 205 having asharp shape can be formed.

[0194] As described above, according to the second embodiment, the phaseshifter (peripheral portion) made of a single layered structure of thelower phase adjusting film 21 is sandwiched by the opening(light-transmitting portion) made of the exposed portion of thetransparent substrate 20 and the semi-light-shielding portion made of amultilayered structure of the lower phase adjusting film 21, thetransmittance adjusting film 22 and the upper phase adjusting film 23.In this case, the multilayered structure of the lower phase adjustingfilm 21, the transmittance adjusting film 22 and the upper phaseadjusting film 23 transmit exposure light in the same phase as that ofthe opening, whereas the single layered structure of the lower phaseadjusting film 21 transmits exposure light in a phase opposite to thatof the opening. Therefore, the contrast in the light intensitydistribution between the opening and the phase shifter can be enhancedby mutual interference between the light transmitted through the openingand the light transmitted through the phase shifter. This contrastenhancement effect also can be obtained when a fine isolatedresist-removed portion (i.e., a fine isolated space patterncorresponding to the light-transmitting portion) is formed with obliqueincident exposure (off-axis illumination), for example, in the positiveresist process. That is to say, it is possible to miniaturize isolatedspace patterns and isolated line patterns or dense patterns at the sametime with oblique incident exposure.

[0195] According to the second embodiment, the lower phase adjustingfilm 21, the transmittance adjusting film 22, the upper phase adjustingfilm 23 that are laminated on the transparent substrate 20 are etchedselectively, so that a mask pattern with any shape that has thesemi-light-shielding portion and the phase shifter (peripheral portion)can be easily produced.

[0196] According to the second embodiment, a phase shifter with anyshape can be formed by processing the transmittance adjusting film 22and the upper phase adjusting film 23 of the multilayered structure ofthe lower phase adjusting film 21, the transmittance adjusting film 22and the upper phase adjusting film 23 constituting thesemi-light-shielding portion. Therefore, as the layout of the outlineenhancement mask, not only the type shown in FIGS. 16B and 16C, that is,the type shown in FIG. 8B, but also all the types shown in FIGS. 8A to8F, for example, can be realized.

[0197] According to the second embodiment, the semi-light-shieldingportion is formed by providing the transmittance adjusting film 22having a lower transmittance than that of the phase adjusting filmsbetween the lower phase adjusting film 21 and the upper phase adjustingfilm 23. Therefore, the difference in the transmittance between thesemi-light-shielding portion and the phase shifter (peripheral portion)made of the single layered structure of the lower phase adjusting film21 can be increased, so that the contrast in the light intensitydistribution between the opening (light-transmitting portion) and theperipheral portion can be enhanced more significantly.

[0198] In the second embodiment, it is preferable that the transmittanceof the semi-light-shielding portion of the photomask is 6% or more and15% or less. Thus, the contrast enhancement effect can be obtainedreliably while preventing a reduction in thickness of the resist film inpattern formation.

[0199] In the second embodiment, the description is based on the use ofthe positive resist process, but the negative resist process can beused, instead of the positive resist process. In this case, in eitherone of the processes, as the exposure light source, the i line(wavelength 365 nm), KrF excimer laser light (wavelength 248 nm), ArFexcimer laser light (wavelength 193 nm), or F₂ excimer laser light(wavelength 157 nm) can be used, for example.

[0200] In the second embodiment, for example, as shown in FIG. 16C, themultilayered structure of the lower phase adjusting film 21, thetransmittance adjusting film 22 and the upper phase adjusting film 23 isused as the semi-light-shielding portion. However, instead of this, forexample, as shown in FIG. 18A, even if a two layered structure of thephase adjusting film 21 as the lower layer and the transmittanceadjusting film 22 as the upper layer is used, the photomask having thesame effect can be realized. More specifically, in the structure shownin FIG. 18A, the phase adjusting film 21 and the transmittance adjustingfilm 22 formed only on the phase adjusting film 21 in thesemi-light-shielding portion formation region constitute thesemi-light-shielding film that transmits exposure light in the samephase as that of the opening. The transmittance adjusting film 22 has arelatively low transmittance with respect to exposure light, whereas thephase adjusting film 21 has a relatively high transmittance. Thus, thesemi-light-shielding film made of the phase adjusting film 21 and thetransmittance adjusting film 22 has a transmittance that allows exposurelight to be transmitted partially. The transmittance adjusting film 22transmits exposure light in the same phase as that of the opening, andthe portion of the phase adjusting film 21 in the semi-light-shieldingportion formation region transmits exposure light in the same phase asthat of the opening. On the other hand, the portion of the phaseadjusting film 21 in the phase shifter (peripheral portion) formationregion is made thin so as to have a thickness that allows exposure lightto be transmitted in the phase opposite to that of the opening. Whencomparing the structure shown in FIG. 16C and the structure shown inFIG. 18A, the structure shown in FIG. 16C is better than the structureshown in FIG. 18A in that the transmittance adjusting film 22 can beutilized as an etching stopper when etching the upper phase adjustingfilm 23 in mask processing. On the other hand, the structure shown inFIG. 18A is better than the structure shown in FIG. 16C in that thephase shifter can be formed by changing the thickness of the phaseadjusting film 21 formed as a single film by etching, in other words, inthat the photomask structure is simple. Furthermore, according to thestructure shown in FIG. 18A, a combination of a desired phase differenceand a desired transmittance can be selected arbitrarily for thesemi-light-shielding film made of the phase adjusting film 21 and thetransmittance adjusting film 22. Moreover, a combination of the materialof the transmittance adjusting film 22 and the material of the phaseadjusting film 21 makes it possible to improve the selection ratio atetching for processing the semi-light-shielding film.

[0201] In the second embodiment, for example, as shown in FIG. 16C, thetransmittance adjusting film 22 is not formed on the lower phaseadjusting film 21 in the phase shifter formation region. However,instead of this, as shown in FIG. 18B, the transmittance adjusting film22 may be formed on the lower phase adjusting film 21 in the phaseshifter formation region. In other words, the phase shifter made of asingle layered structure of the lower phase adjusting film 21 can bereplaced by a phase shifter made of a multilayered structure of thelower phase adjusting film 21 and the transmittance adjusting film 22.In this case, the transmittance of the phase shifter and thetransmittance of the semi-light-shielding portion are in the same level.When comparing the structure shown in FIG. 16C and the structure shownin FIG. 18B, the structure shown in FIG. 16C is better than thestructure shown in FIG. 18B in that the transmittance of thesemi-light-shielding portion is higher than that of the phase shifter,that is, in that the contrast enhancement effect by the outlineenhancement method is improved. On the other hand, the structure shownin FIG. 18B is better than the structure shown in FIG. 16C in that thesize of the phase shifter can be increased to the extent correspondingto how low the transmittance of the phase shifter is, that is, in thatthe mask processing is easy.

[0202] Furthermore, a photomask having the same effect can be realized,even if a two layered structure of the transmittance adjusting film 22as the lower layer and the phase adjusting film 23 as the upper layer isused as the semi-light-shielding portion and the phase shifter, forexample, as shown in FIG. 18C, instead of the structure shown in FIG.18B. More specifically, in the structure shown in FIG. 18C, thetransmittance adjusting film 22 and the phase adjusting film 23 in thesemi-light-shielding portion formation region constitute asemi-light-shielding film that transmits exposure light in the samephase as that of the opening. Furthermore, the transmittance adjustingfilm 22 has a relatively low transmittance with respect to exposurelight, whereas the phase adjusting film 23 has a relatively hightransmittance with respect to exposure light. Thus, thesemi-light-shielding film made of the transmittance adjusting film 22and the phase adjusting film 23 has a transmittance that allows exposurelight to be transmitted partially. The transmittance adjusting film 22transmits exposure light in the same phase as that of the opening, andthe portion of the phase adjusting film 23 in the semi-light-shieldingportion formation region transmits exposure light in the same phase asthat of the opening. On the other hand, the portion of the phaseadjusting film 23 in the phase shifter (peripheral portion) formationregion is made thin so as to have a thickness that allows exposure lightto be transmitted in the phase opposite to that of the opening. Whencomparing the structure shown in FIG. 18B and the structure shown inFIG. 18C, the structure shown in FIG. 18C is better in that thephotomask structure is simple. In addition, in the case where the phaseadjusting film 23 is formed of a material that hardly can increase theetching selection ratio with respect to the transparent substrate 20made of quartz or the like, the structure shown in FIG. 18C is better inthat the transmittance adjusting film 22 can be utilized as an etchingstopper for preventing etching of quartz when etching the phaseadjusting film 23. Furthermore, according to the structure shown in FIG.18C, a combination of a desired phase difference and a desiredtransmittance can be selected arbitrarily for the semi-light-shieldingfilm made of the phase adjusting film 23 and the transmittance adjustingfilm 22. Moreover, a combination of the material of the transmittanceadjusting film 22 and the material of the phase adjusting film 23 makesit possible to improve the selection ratio at etching for processing thesemi-light-shielding film.

[0203] In the second embodiment, as seen from the comparison of thestructure shown in FIG. 16C and the structure shown in FIG. 18B, phaseshifters having different transmittances can be formed with the samemultilayered structure in which the transmittance adjusting film 22 ispresent between the lower phase adjusting film 21 and the upper phaseadjusting film 23 by changing the processing method of the transmittanceadjusting film 22. In other words, when the structure in which thetransmittance adjusting film is sandwiched by the two phase adjustingfilms is used, both the structure shown in FIG. 16C and the structureshown in FIG. 18B can be realized in the same photomask, so that thetransmittance of the phase shifter (peripheral portion) can be changeddepending on the pattern shape. Furthermore, for example, as shown inFIG. 18D, when the structure in which the transmittance adjusting film22 is formed partially on the lower phase adjusting film 21 in the phaseshifter formation region is used, the effective transmittance of thephase shifter can be adjusted finely by the area ratio of the phaseshifter that is covered with the transmittance adjusting film 22 (=(thearea of the transmittance adjusting film 22 in the phase shifterformation region)/(the area of the phase shifter)). Therefore, it ispossible to arbitrarily change the transmittance of the phase shifterdepending on the pattern shape on the same photomask.

[0204] Third Embodiment

[0205] Hereinafter, a photomask according to a third embodiment of thepresent invention, a method for producing the photomask and a method forforming a pattern using the photomask will be described with referenceto the accompanying drawings. The photomask of the third embodiment is aphotomask of a reduction projection exposure system to realize theabove-described outline enhancement method.

[0206]FIG. 19A shows an example of a desired pattern to be formed withthe photomask of the third embodiment. In this embodiment as well as thefirst embodiment, the description is based on the assumption that thepositive resist process is used. In this embodiment, the transmittanceis expressed by an effective transmittance when the transmittance of thetransparent substrate is taken as 100%, unless otherwise specified.

[0207]FIG. 19B is a plan view of the photomask of the third embodiment,more specifically, a photomask for forming the desired pattern shown inFIG. 19A. As shown in FIG. 19B, openings (light-transmitting portions)are provided so as to correspond to resist-removed portions in thedesired pattern. Furthermore, a semi-light-shielding portion that has alow transmittance (about 6 to 15%) that does not allow the resist filmto be exposed and transmits exposure light in the same phase as that ofthe opening is used as the light-shielding mask pattern surrounding theopening, instead of the complete light-shielding portion that completelyshields exposure light. Furthermore, phase shifters (peripheralportions) that transmit exposure light in a phase opposite to that ofthe openings are provided in the periphery of the openings. In thisembodiment, the transmittance of the phase shifter is set to a highervalue than that of the semi-light-shielding portion so that the lighttransmitted through the phase shifters can cancel effectively the lightstransmitted through the openings and the semi-light-shielding portion,according to the principle of the outline enhancement method.

[0208] In the third embodiment, the phase shifters are arranged in sucha manner that the sides of the phase shifters are in contact with thecorresponding sides of the rectangular opening in a region having apredetermine size or less from each side of the rectangular opening, forexample, as shown in FIG. 8B.

[0209]FIG. 19C is a cross-sectional view taken along line AA′ in FIG.19B, that is a cross-sectional view of the photomask of the thirdembodiment. As shown in FIG. 19C, the surface of the transparentsubstrate 30 in the opening formation region is exposed. Asemi-light-shielding film (half-tone film) 31 having a low transmittance(about 6 to 15%) that does not allow the resist film to be exposed isformed on the transparent substrate 30 in the semi-light-shieldingportion formation region and the phase shifter formation region. As theportion of the half-tone film 31, an oxide film such as ZrSiO, CrAlO,TaSiO, MoSiO or TiSiO can be used. The portion of the half-tone film 31in the semi-light-shielding portion formation region has a thicknessthat causes a phase difference (the same phase) of 360 degrees (morespecifically, (−30+360×n) degrees or more and (30+360×n) degrees or less(where n=an integer)) with respect to exposure light between this filmand the transparent substrate 30 (opening). On the other hand, theportion of the half-tone film 31 in the phase shifter formation regionhas a small thickness that causes a phase difference (opposite phase) of(150+360×n) degrees or more and (210+360×n) degrees or less (where n isan integer) between this film and the opening. That is to say, thehalf-tone film 31 can transmit exposure light in a phase opposite tothat of the opening when its thickness is changed.

[0210] As described above, in the photomask of this embodiment, theperipheral portion, that is, the phase shifter, made of a thin portionof the half-tone film 31 is formed between the semi-light-shieldingportion made of a thick portion of the half-tone film 31 and the opening(light-transmitting portion), and thus the function of the outlineenhancement mask is realized. However, in this phase shifter, bydecreasing the thickness of the half-tone phase film 31, phase inversionoccurs and the transmittance with respect to exposure light is madelarger than that of the semi-light-shielding portion made of the thickportion of the half-tone film 31. Furthermore, it is necessary to limitthe width of the phase shifter to a predetermined size or less in orderto enhance the contrast by the outline enhancement method.

[0211] A method for producing the photomask of the third embodiment isas follows. The half-tone film 31 is formed on the transparent substrate30 made of a material having light-transmitting properties with respectto exposure light (e.g., quartz). Thereafter, the half-tone film 31 isselectively etched.

[0212] Next, a method for forming a pattern using the photomask of thethird embodiment will be described. In this case, as described withreference to the principle of the outline enhancement method whentransferring a mask pattern in a reduced size with an exposureapparatus, it is preferable to use an oblique incident exposure lightsource as shown in FIGS. 11B to 11D in order to form an image having ahigh contrast with the outline enhancement mask.

[0213]FIGS. 20A to 20D are cross-sectional views showing the processesof a method forming a pattern with the photomask of the thirdembodiment.

[0214] First, as shown in FIG. 20A, after a film 301 to be processedsuch as a metal film or an insulating film is formed on a substrate 300,as shown in FIG. 20B, a positive resist film 302 is formed on the film301 to be processed.

[0215] Next, as shown in FIG. 20C, the photomask of the third embodimentincluding the semi-light-shielding portion made of the thick portion ofthe half-tone film 31 and the phase shifter made of the thin portion ofthe half-tone film 31 is irradiated with exposure light 303 with anoblique incident exposure light source to expose the resist film 302with transmitted light 304 transmitted through the photomask. In thiscase, as the mask pattern, the semi-light-shielding portion having a lowtransmittance is used, so that the entire resist film 302 is exposedwith weak energy. However, as shown in FIG. 20C, only a latent imageportion 302 a of the resist film 302 corresponding to thelight-transmitting portion (opening) in the photomask is irradiated withexposure energy that is sufficient to dissolve the resist film 302 in adeveloping process.

[0216] Next, the latent image portion 302 a is removed by performingdevelopment with respect to the resist film 302, so that as shown inFIG. 20D, a resist pattern 305 is formed. In this case, in the exposureprocess shown in FIG. 20C, light around the opening is canceled, so thata portion corresponding to the phase shifter (peripheral portion) in theresist film 302 is substantially not irradiated with exposure energy.Therefore, the contrast in the light intensity distribution between thelight transmitted through the opening and the light transmitted throughthe peripheral portion, in other words, the contrast in the lightintensity distribution between the light with which the latent imageportion 302 a is irradiated and the light with which the periphery ofthe latent portion 302 a is irradiated can be enhanced. Therefore, theenergy distribution in the latent portion 302 a is changed sharply, sothat a resist pattern 305 having a sharp shape can be formed.

[0217] As described above, according to the third embodiment, the phaseshifter (peripheral portion) made of the thin portion of the half-tonefilm 31 is sandwiched by the opening (light-transmitting portion) madeof the exposed portion of the transparent substrate 30 and thesemi-light-shielding portion made of the thick portion of the half-tonefilm 31. In this case, the thick portion of the half-tone film 31transmits exposure light in the same phase as that of the opening,whereas the thin portion of the half-tone film 31 transmits exposurelight in a phase opposite to that of the opening. Therefore, thecontrast in the light intensity distribution between the opening and thephase shifter can be enhanced by mutual interference between the lighttransmitted through the opening and the light transmitted through thephase shifter. This contrast enhancement effect also can be obtainedwhen a fine isolated resist-removed portion (i.e., a fine isolated spacepattern corresponding to the light-transmitting portion) is formed withoblique incident exposure, for example, in the positive resist process.That is to say, it is possible to miniaturize isolated space patternsand isolated line patterns or dense patterns at the same time withoblique incident exposure.

[0218] According to the third embodiment, the semi-light-shieldingportion is constituted by a single layered structure of the half-tonefilm 31, so that the mask structure is very simple. Moreover, a phaseshifter (peripheral portion) can be formed easily simply by partiallyreducing the thickness of the half-tone film 31, in other words, byproviding a recess in the half-tone film 31.

[0219] According to the third embodiment, the half-tone film 31 formedon the transparent substrate 30 is etched selectively, so that a maskpattern with any shape that has the semi-light-shielding portion and thephase shifter can be easily produced.

[0220] According to the third embodiment, a phase shifter with any shapecan be formed by processing the half-tone film 31 serving as thesemi-light-shielding portion. Therefore, as the layout of the outlineenhancement mask, not only the type shown in FIGS. 19B and 19C, that is,the type shown in FIG. 8B, but also all the types shown in FIGS. 8A to8F, for example, can be realized.

[0221] In the third embodiment, it is preferable that the transmittanceof the semi-light-shielding portion of the photomask is 6% or more and15% or less. Thus, the contrast enhancement effect can be obtainedreliably while preventing a reduction in thickness of the resist film inpattern formation.

[0222] In the third embodiment, the description is based on the use ofthe positive resist process, but the negative resist process can beused, instead of the positive resist process. In this case, in eitherone of the processes, as the exposure light source, the i line(wavelength 365 nm), KrF excimer laser light (wavelength 248 nm), ArFexcimer laser light (wavelength 193 nm), or F₂ excimer laser light(wavelength 157 nm) can be used, for example.

[0223] In the third embodiment, for example, a two layered structure inwhich the transmittance adjusting film having a low transmittance andthe phase adjusting film having a high transmittance are laminated canbe used as the structure of the half-tone film 31 (see FIGS. 18A and18C). By doing this, a combination of a desired phase difference and adesired transmittance can be selected arbitrarily for the half-tone film31. Moreover, the selection ratio at etching for processing thehalf-tone film 31 can be improved by a combination of the material ofthe transmittance adjusting film and the material of the phase adjustingfilm.

[0224] In the third embodiment, as shown in the plan view of FIG. 21Aand the corresponding cross-sectional view of FIG. 21B, the phaseshifter (peripheral portion) made of the thin portion of the half-tonefilm 31 is in contact with the opening (light-transmitting portion).However, instead of this, for example, as shown in the plan view of FIG.21C and the corresponding cross-sectional view of FIG. 21D, the thinportion of the half-tone film 31 can be spaced apart from the opening bya predetermined size. In other words, the phase shifter and the openingare spaced apart from each other, and a semi-light-shielding portionmade of the thick portion of the half-tone film 31 can be formed betweenthe phase shifter and the opening. In this case, as shown in FIGS. 21Cand 21D, a phase shifter can be formed simply by partially reducing thethickness of the half-tone film 31, in other words, by providing arecess in the half-tone film 31. As a result, also in the case where asemi-light-shielding portion having a small width is present between thephase shifter and the opening, peeling of the film constituting thesemi-light-shielding portion having a small width can be suppressedbetter, compared with the case where a semi-light-shielding portion of amultilayered film structure is used. On the other hand, when thesemi-light-shielding portion with a small width having a multilayeredstructure is provided between the phase shifter and the opening, thesemi-light-shielding portion is present as a small isolated region ofthe upper film formed on the lower film, so that the isolated regiontends to be peeled while processing the upper film.

[0225] Fourth Embodiment

[0226] Hereinafter, a photomask according to a fourth embodiment of thepresent invention, a method for producing the photomask and a method forforming a pattern using the photomask will be described with referenceto the accompanying drawings. The photomask of the fourth embodiment isa photomask of a reduction projection exposure system to realize theabove-described outline enhancement method.

[0227]FIG. 22A shows an example of a desired pattern to be formed withthe photomask of the fourth embodiment. In this embodiment as well asthe first embodiment, the description is based on the assumption thatthe positive resist process is used. In this embodiment, thetransmittance is expressed by an effective transmittance when thetransmittance of the transparent substrate is taken as 100%, unlessotherwise specified.

[0228]FIG. 22B is a plan view of the photomask of the fourth embodiment,more specifically, a photomask for forming the desired pattern shown inFIG. 22A. As shown in FIG. 22B, openings (light-transmitting portions)are provided so as to correspond to resist-removed portions in thedesired pattern. Furthermore, a semi-light-shielding portion that has alow transmittance (about 6 to 15%) that does not allow the resist filmto be exposed and transmits exposure light in the same phase as that ofthe opening is used as the light-shielding mask pattern surrounding theopening, instead of the complete light-shielding portion that completelyshields exposure light. Furthermore, phase shifters (peripheralportions) that transmit exposure light in a phase opposite to that ofthe openings are provided in the periphery of the openings. In thisembodiment, the transmittance of the phase shifter is set to a highervalue than that of the semi-light-shielding portion so that the lighttransmitted through the phase shifters can cancel effectively the lightstransmitted through the openings and the semi-light-shielding portion,according to the principle of the outline enhancement method.

[0229] In the fourth embodiment, the phase shifters are arranged in sucha manner that the sides of the phase shifters are in contact with thecorresponding sides of the rectangular opening in a region having apredetermine size or less from each side of the rectangular opening, forexample, as shown in FIG. 8B.

[0230]FIG. 22C is a cross-sectional view taken along line AA′ in FIG.22B, that is a cross-sectional view of the photomask of the fourthembodiment. As shown in FIG. 22C, the surface of the transparentsubstrate 40 in the opening formation region is exposed. Asemi-light-shielding film (half-tone film) 41 having a low transmittance(about 6 to 15%) that does not allow the resist film to be exposed isformed on the transparent substrate 40 in the semi-light-shieldingportion formation region. The half-tone film 41 generates a phasedifference (the same phase) of 360 degrees with respect to exposurelight (more specifically, (−30+360×n) degrees or more and (30+360×n)degrees or less, (where n=an integer)) between this film and thetransparent substrate 40 (opening). The portion of the transparentsubstrate 40 in the phase shifter formation region is dug down so as tohave a thickness that causes a phase difference (opposite phase) of(150+360×n) degrees or more and (210+360×n) degrees or less (where n isan integer) between this film and the opening. That is to say, the dugportion 40 a is provided in the transparent substrate 40 in the phaseshifter formation region.

[0231] As the half-tone film 41, a thin film (having a thickness of 30nm or less) made of a metal such as Zr, Cr, Ta, Mo or Ti or a thin film(having a thickness of 30 nm or less) made of a metal alloy such as aTa—Cr alloy, a Zr—Si alloy, a Mo—Si alloy or a Ti—Si alloy can be used.In this embodiment, as the half-tone film 41, for example, a singlelayered structure of a light-shielding film (e.g., a chromium film usedas a light-shielding film of a regular photomask) that is made thin soas to have a very small phase difference between this film and theopening and thus has a low transmittance that does not allow the resistfilm to be exposed is used.

[0232] As described above, according to the photomask of thisembodiment, the phase shifter made of the dug portion 40 a of thetransparent substrate 40 is formed between the semi-light-shieldingportion made of the half-tone film 41 and the opening(light-transmitting portion), and thus the function of the outlineenhancement mask is realized. However, it is necessary to limit thewidth of the phase shifter to a predetermined size or less in order toenhance the contrast by the outline enhancement method.

[0233] Next, a method for forming a pattern using the photomask of thefourth embodiment will be described. In this case, as described withreference to the principle of the outline enhancement method whentransferring a mask pattern in a reduced size with an exposureapparatus, it is preferable to use an oblique incident exposure lightsource as shown in FIGS. 11B to 11D in order to form an image having ahigh contrast with the outline enhancement mask.

[0234]FIGS. 23A to 23D are cross-sectional views showing the processesof a method forming a pattern with the photomask of the fourthembodiment.

[0235] First, as shown in FIG. 23A, after a film 401 to be processedsuch as a metal film or an insulating film is formed on a substrate 400,as shown in FIG. 23B, a positive resist film 402 is formed on the film401 to be processed.

[0236] Next, as shown in FIG. 23C, the photomask of the fourthembodiment including the semi-light-shielding portion made of thehalf-tone film 41 and the phase shifter (peripheral portion) made of thedug portion 40 a of the transparent substrate 40 is irradiated withexposure light 403 with an oblique incident exposure light source toexpose the resist film 402 with transmitted light 404 transmittedthrough the photomask. In this case, as the mask pattern, thesemi-light-shielding portion having a low transmittance is used, so thatthe entire resist film 402 is exposed with weak energy. However, asshown in FIG. 23C, only a latent image portion 402 a of the resist film402 corresponding to the light-transmitting portion (opening) in thephotomask is irradiated with exposure energy that is sufficient todissolve the resist film 402 in a developing process.

[0237] Next, the latent image portion 402 a is removed by performingdevelopment with respect to the resist film 402, so that as shown inFIG. 23D, a resist pattern 405 is formed. In this case, in the exposureprocess shown in FIG. 23C, light around the opening is canceled, so thata portion corresponding to the phase shifter (peripheral portion) in theresist film 402 is substantially not irradiated with exposure energy.Therefore, the contrast in the light intensity distribution between thelight transmitted through the opening and the light transmitted throughthe peripheral portion, in other words, the contrast in the lightintensity distribution between the light with which the latent imageportion 402 a is irradiated and the light with which the periphery ofthe latent portion 402 a is irradiated can be enhanced. Therefore, theenergy distribution in the latent portion 402 a is changed sharply, sothat a resist pattern 405 having a sharp shape can be formed.

[0238] Next, a method for producing a photomask of the fourth embodimentwill be described with reference to the drawings.

[0239]FIGS. 24A to 24E are cross-sectional views showing the processesof a method for producing the photomask of the fourth embodiment. FIG.24F is a plan view corresponding to the cross-sectional view of FIG.24C. FIG. 24G is a plan view corresponding to the cross-sectional viewof FIG. 24E.

[0240] First, as shown in FIG. 24A, the half-tone film 41 is formed onthe transparent substrate 40 made of a material havinglight-transmitting properties with respect to exposure light such asquartz. As the half-tone film 41, a single layered light-shielding filmwith a reduced thickness is used.

[0241] Next, as shown in FIG. 24B, a first resist pattern 42 that coversthe semi-light-shielding portion formation region and the opening(light-transmitting portion) formation region is formed on thetransparent substrate 40. That is, a first resist pattern 42 having aremoved portion in the phase shifter (peripheral portion) formationregion is formed on the transparent substrate 40. Thereafter, thehalf-tone film 41 and the transparent substrate 40 are etched with thefirst resist pattern 42 as a mask, and then the first resist pattern 42is removed. Thus, as shown in FIGS. 24C and 24F, the portionscorresponding to the phase shifter formation region in the half-tonefilm 41 are removed. The transparent substrate 40 in the phase shifterformation region is dug down so as to have a thickness that transmitsexposure light in a phase opposite to that of the opening. Morespecifically, a dug portion 40 a that causes phase inversion of 180degrees (more specifically, a phase difference of (150+360×n) degrees ormore and (210+360×n) degrees or less, where n=an integer) in the portioncorresponding to the phase shifter formation region in the transparentsubstrate 40.

[0242] Next, as shown in FIG. 24D, a second resist pattern 43 thatcovers the portion corresponding to the semi-light-shielding portionformation region in the half-tone film 41 is formed on the transparentsubstrate 40. Thereafter, the half-tone film 41 is etched with thesecond resist pattern 43 as a mask, and then the second resist pattern43 is removed. Thus, as shown in FIGS. 24E and 24G, the portioncorresponding to the opening formation region in the half-tone film 41is removed, and thus the photomask of the fourth embodiment iscompleted. That is to say, the photomask of the fourth embodiment havingthe plane structure of the outline enhancement mask can be easily formedby, as a mask blank, preparing a transparent substrate in which alight-shielding film with a reduced thickness is deposited, and thenperforming etching with respect to the light-shielding film and thetransparent substrate sequentially.

[0243] As described above, according to the fourth embodiment, the phaseshifter (peripheral portion) made of the dug portion 40 a in thetransparent substrate 40 is sandwiched by the opening(light-transmitting portion) made of the exposed portion of thetransparent substrate 40 and the semi-light-shielding portion made ofthe half-tone film 41. The half-tone film 41 transmits exposure light inthe same phase as that of the opening, whereas the dug portion 40 atransmits exposure light in a phase opposite to that of the opening.Therefore, the contrast in the light intensity distribution between theopening and the phase shifter can be enhanced by mutual interferencebetween the light transmitted through the opening and the lighttransmitted through the phase shifter. This contrast enhancement effectalso can be obtained when a fine isolated resist-removed portion (i.e.,a fine isolated space pattern corresponding to the light-transmittingportion) is formed with oblique incident exposure, for example, in thepositive resist process. That is to say, it is possible to miniaturizeisolated space patterns and isolated line patterns or dense patterns atthe same time with oblique incident exposure.

[0244] According to the fourth embodiment, the semi-light-shieldingportion is constituted by a single layered structure of the half-tonefilm 41, so that the mask structure is simple.

[0245] According to the fourth embodiment, after the half-tone film 41is formed on the transparent substrate 40, the half-tone film 41 and thetransparent substrate 40 are etched selectively, so that a mask patternwith any shape that has the semi-light-shielding portion and the phaseshifter (peripheral portion) can be easily realized.

[0246] According to the fourth embodiment, a phase shifter with anyshape can be formed by processing the multilayered structure of thetransparent substrate 40 and the half-tone film 41 by the method forproducing a photomask shown in, for example, FIGS. 24A to 24E.Therefore, as the pattern layout of the outline enhancement mask, notonly the type shown in FIGS. 22B and 22C, that is, the type shown inFIG. 8B, but also all the types shown in FIGS. 8A to 8F, for example,can be realized.

[0247] According to the fourth embodiment, as the half-tone film 41, afilm obtained by reducing the thickness of a light-shielding film for aregular photomask is used, so that a substrate to be prepared as a maskblank can be simplified. That is to say, photomask process can beperformed easily only by preparing a transparent substrate in which asingle layered thin film is formed as a mask blank, and etching each ofthe single layered thin film and the transparent substrate. For example,the transparent substrate in which a two layered structure of a phaseadjusting film and a transmittance adjusting film is formed is used as amask blank for a regular half-tone phase-shifting mask. However, in thisembodiment, a half-tone phase-shifting mask in which the phase adjustingfilm is not formed, in other words, a mask blank in which only thetransmittance adjusting film is formed on the transparent substrate canbe used. That is to say, a conventional technology can be utilized inproduction of a mask blank by using a light-shielding film with areduced thickness as the half-tone film 41, which is advantageous inpractice.

[0248] Hereinafter, the results of examination with simulations of aninfluence of a phase change (a phase difference caused between theopening and the semi-light-shielding portion) due to the use of thelight-shielding film with a reduced thickness as the half-tone phasefilm 41, that is, the semi-light-shielding portion on the patternformation will be described with reference to FIGS. 25A to 25C. Thesimulation conditions are such that the wavelength λ of the exposurelight is 0.193 μm (ArF light source), the numerical aperture NA of theprojection optical system of the exposure apparatus is 0.6, and annularillumination is used.

[0249]FIG. 25A shows a plan view of an outline enhancement mask used inthe simulations. As shown in FIG. 25A, the width of the opening and thephase shifter is 200 nm and 50 nm, respectively. The transmittance ofthe opening, the phase shifter and the semi-light-shielding portion is100%, 100% and 7.5%, respectively. The phase shifter generates a phasedifference of 180 degrees between this portion and the opening, and thesemi-light-shielding portion generates a phase difference of 0 to 30degrees between this portion and the opening.

[0250]FIG. 25B shows the simulation results of the light intensitydistribution corresponding to line AA′ when exposure is performed withrespect to the outline enhancement mask shown in FIG. 25A in such amanner that a phase difference of 0 degrees, 10 degrees, 20 degrees or30 degrees is generated between the semi-light-shielding portion and theopening. As shown in FIG. 25B, if the phase difference between thesemi-light-shielding portion and the opening is not more than 30 degreeor so, the contrast in the light intensity distribution is notsubstantially affected.

[0251]FIG. 25C shows the simulation results of the focus dependence ofthe size (CD: Critical Dimension) of the finished pattern when exposureis performed with respect to the outline enhancement mask shown in FIG.25A in such a manner that a phase differences of 0 degrees, 10 degrees,20 degrees or 30 degrees is generated between the semi-light-shieldingportion and the opening. As shown in FIG. 25C, if the phase differencebetween the semi-light-shielding portion and the opening is changed, thebest focus position in which the CD is the peak is changed. However,even if the phase difference is changed, the unlikelihood of CD changewith respect to the focus variation, that is, the depth of focus issubstantially not changed. No problem is caused in pattern formation,even if the best focus positions are varied in the same manner, at allportions on the photomask. Only the depth of focus is an issue inpattern formation. That is to say, if the phase difference between thesemi-light-shielding portion and the opening is up to about 30 degrees,there is no problem in terms of the focus characteristics.

[0252] Therefore, in this embodiment, when a light-shielding film with areduced thickness is used as the half-tone film 41 serving as asemi-light-shielding portion, the outline enhancement mask in a strictsense (the phase difference between the semi-light-shielding portion andthe opening is 0 degree) cannot be realized, but if the phase differencethat is caused by the reduction of the film is about 30 degrees or less,the effect of the outline enhancement method is not lost. Morespecifically, when Ta, Cr or alloys containing Ta or Cr or the like isused as the material of the light-shielding film, the thickness of thelight-shielding film that generates a phase difference of about 30degrees between this film and the opening with respect to light from anArF light source is approximately 30 nm or more. This thickness issufficient to realize a transmittance of 10% or less.

[0253] In the fourth embodiment, it is preferable that the transmittanceof the semi-light-shielding portion is 6% or more and 15% or less. Thus,the contrast enhancement effect can be obtained reliably whilepreventing a reduction in thickness of the resist film in patternformation.

[0254] In the fourth embodiment, the description is based on the use ofthe positive resist process, but the negative resist process can beused, instead of the positive resist process. In this case, in eitherone of the processes, as the exposure light source, the i line(wavelength 365 nm), KrF excimer laser light (wavelength 248 nm), ArFexcimer laser light (wavelength 193 nm), or F₂ excimer laser light(wavelength 157 nm) can be used, for example.

[0255] In the fourth embodiment, for example, a two layered structure inwhich the transmittance adjusting film having a low transmittance andthe phase adjusting film having a high transmittance are laminated canbe used as the structure of the half-tone film 41. By doing this, acombination of a desired phase difference (more specifically (−30+360×n)degrees or more and (30+360×n) degrees or less) and a desiredtransmittance can be selected arbitrarily for the half-tone film 41.Moreover, the selection ratio at etching for processing the half-tonefilm 41 can be improved by a combination of the material of thetransmittance adjusting film and the material of the phase adjustingfilm. Furthermore, for example, it is possible to set a phase differencebetween the opening and the semi-light-shielding portion to 0 degree bydepositing a phase adjusting film on the single layered thinlight-shielding film used as the half-tone film 41 in this embodiment.

[0256] In the fourth embodiment, as shown in the plan view of FIG. 22Band the corresponding cross-sectional view of FIG. 22C, the dug portion40 a in the transparent substrate 40, that is, the phase shifter is incontact with the opening. However, instead of this, for example, asshown in the plan view of FIG. 26A and the corresponding cross-sectionalview of FIG. 26B, the half-tone film 41 is used as thesemi-light-shielding portion, and the dug portion 40 a in thetransparent substrate 40 can be spaced apart from the opening by apredetermined size. In other words, the phase shifter (peripheralportion) and the opening (light-transmitting portion) are spaced apartfrom each other, and a semi-light-shielding portion can be formedbetween the phase shifter and the opening. FIG. 26C shows across-sectional structure of a photomask using a semi-light shieldingportion in which the phase adjusting film is deposited on a singlelayered thin film having a low transmittance, instead of thesemi-light-shielding portion constituted only by the half-tone film 41in the photomask shown in FIG. 26B. In the photomask shown in the planview of FIG. 26C, a two layered structure in which a transmittanceadjusting film 41A having a low transmittance and a phase adjusting film41B having a high transmittance are laminated is used as thesemi-light-shielding portion, and thus the phase difference between thesemi-light-shielding portion and the opening is set to 0 degree. As thetransmittance adjusting film 41A, a thin film (having a thickness of 30nm or less) made of a metal such as Zr, Cr, Ta, Mo or Ti or a thin film(having a thickness of 30 nm or less) made of a metal alloy such as aTa—Cr alloy, a Zr—Si alloy, a Mo—Si alloy or a Ti—Si alloy can be used.As the phase adjusting film 41B, an oxide film such as SiO₂ film can beused.

[0257] As the photomask shown in FIG. 26C, when the semi-light-shieldingportion having a small width that spaces the phase shifter apart fromthe opening constitutes a thick multilayered film structure, morespecifically, a small isolated region of a thick phase adjusting film41B formed on the lower transmittance adjusting film 41A is presentbetween the phase shifter and the opening, the isolated region tends tobe peeled during the processing of the phase adjusting film 41B. Asopposed to this, the cross-sectional structure of the photomask can besuch as shown in FIG. 26D by utilizing the advantage that no problem iscaused if a phase difference of up to 30 degrees is generated betweenthe phase shifter and the opening. That is to say, a single layeredstructure of a thin transmittance adjusting film 41A that is notprovided with the phase adjusting film 41B can be used as thesemi-light-shielding portion having a small width between the phaseshifter and the opening. The single layered structure of thetransmittance adjusting film 41A generates a small phase differencebetween this structure and the opening. Thus, also when asemi-light-shielding portion having a small width is present between thephase shifter and the opening, a photomask having an effect of theoutline enhancement method can be formed while suppressing peeling ofthe film constituting the semi-light-shielding portion having a smallwidth. For example, in this embodiment, the half-tone film 41 made ofthe single layered thin light-shielding film is used for the entiresemi-light-shielding portion formation region. However, instead of this,the single layered structure of half-tone film 41 is used as thesemi-light-shielding portion between the phase shifter and the opening,and the multilayered structure of the half-tone film 41 and the phaseadjusting film formed thereon can be used as the semi-light-shieldingportion for the other regions.

[0258] In the first to fourth embodiments, it is assumed that all theportions except the opening (light-transmitting portion) and the phaseshifter (peripheral portion) in the photomask are semi-light-shieldingportions. However, the portion in the photomask that is apart from eachof the opening and the phase shifter by a sufficient distance, that is,a distance (=2×λ/NA (λ is the wavelength of exposure light, and NA isthe numerical aperture of a reduction projection optical system of anexposure apparatus)) that allows an influence of optical interferenceeffects from each of the opening and the phase shifter to be ignored maybe a complete light-shielding portion.

[0259] The invention may be embodied in other forms without departingfrom the spirit or essential characteristics thereof. The embodimentsdisclosed in this application are to be considered in all respects asillustrative and not limiting. The scope of the invention is indicatedby the appended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

What is claimed is:
 1. A photomask comprising on a transparentsubstrate: a semi-light-shielding portion having a light-shieldingproperty with respect to exposure light: a light-transmitting portionsurrounded by the semi-light-shielding portion and having alight-transmitting property with respect to exposure light: and aperipheral portion surrounded by the semi-light-shielding portion andpositioned in a periphery of the light-transmitting portion, wherein thesemi-light-shielding portion and the light-transmitting portion transmitthe exposure light in a same phase, the peripheral portion transmits theexposure light in a phase opposite to that of the semi-light-shieldingportion and the light-transmitting portion, a surface of the transparentsubstrate in a formation region for the light-transmitting portion isexposed, a first phase shift film that transmits the exposure light in aphase opposite to that of the light-transmitting portion is formed onthe transparent substrate in a formation region for the peripheralportion, the first phase shift film and a second phase shift film thattransmits the exposure light in a phase opposite to that of thelight-transmitting portion are laminated sequentially on the transparentsubstrate in a formation region for the semi-light-shielding portion,and a multilayered structure of the first phase shift film and thesecond phase shift film has a transmittance that allows the exposurelight to be transmitted partially and transmits the exposure light in asame phase as that of the light-transmitting portion.
 2. The photomaskaccording to claim 1, wherein the first phase shift film has a firsttransmittance adjusting film and a first phase adjusting film formed onthe first transmittance adjusting film, the first transmittanceadjusting film transmits the exposure light in a same phase as that ofthe light-transmitting portion and has a relatively low transmittancewith respect to the exposure light, and the first phase adjusting filmtransmits the exposure light in a phase opposite to that of thelight-transmitting portion and has a relatively high transmittance withrespect to the exposure light.
 3. The photomask according to claim 1,wherein the second phase shift film has a second transmittance adjustingfilm and a second phase adjusting film formed on the secondtransmittance adjusting film, the second transmittance adjusting filmtransmits the exposure light in a same phase as that of thelight-transmitting portion and has a relatively low transmittance withrespect to the exposure light, and the second phase adjusting filmtransmits the exposure light in a phase opposite to that of thelight-transmitting portion and has a relatively high transmittance withrespect to the exposure light.
 4. The photomask according to claim 1,wherein the peripheral portion is in contact with the light-transmittingportion.
 5. The photomask according to claim 1, wherein the peripheralportion is spaced apart from the light-transmitting portion by apredetermined distance.
 6. The photomask according to claim 1, whereinthe first phase shift film has a first phase adjusting film thattransmits the exposure light in a phase opposite to that of thelight-transmitting portion, the second phase shift film has a secondphase adjusting film that is formed on the first phase adjusting filmand transmits the exposure light in a phase opposite to that of thelight-transmitting portion, and a transmittance adjusting film having alower transmittance than that of the phase adjusting films with respectto the exposure light is formed between the first phase adjusting filmand the second phase adjusting film.
 7. The photomask according to claim1, wherein a transmittance of the semi-light-shielding portion withrespect to the exposure light is 6% or more and 15% or less.
 8. A methodfor forming a pattern that uses the photomask according to claim 1,comprising the steps of: forming a resist film on a substrate;irradiating the resist film with the exposure light via the photomask,and developing the resist film irradiated with the exposure light so asto pattern the resist film.
 9. The method for forming a patternaccording to claim 8, off-axis illumination is used in the step ofirradiating the resist film with the exposure light.
 10. A photomaskcomprising on a transparent substrate: a semi-light-shielding portionhaving a light-shielding property with respect to exposure light: alight-transmitting portion surrounded by the semi-light-shieldingportion and having a light-transmitting property with respect toexposure light: and a peripheral portion surrounded by thesemi-light-shielding portion and positioned in a periphery of thelight-transmitting portion, wherein the semi-light-shielding portion andthe light-transmitting portion transmit the exposure light in a samephase, the peripheral portion transmits the exposure light in a phaseopposite to that of the semi-light-shielding portion and thelight-transmitting portion, a surface of the transparent substrate in aformation region for the light-transmitting portion is exposed, asemi-light-shielding film that has a transmittance allowing the exposurelight to be transmitted partially and transmits the exposure light in asame phase to that of the light-transmitting portion is formed on thetransparent substrate in the semi-light-shielding portion formationregion, and the semi-light-shielding film with a reduced thickness isformed on the transparent substrate in a formation region for theperipheral portion, the thickness being such an extent that the exposurelight is transmitted in a phase opposite to that of thelight-transmitting portion.
 11. The photomask according to claim 10,wherein the semi-light-shielding film has a transmittance adjusting filmformed on the transparent substrate and a phase adjusting film formed onthe transmittance adjusting film, the transmittance adjusting filmtransmits the exposure light in a same phase as that of thelight-transmitting portion and has a relatively low transmittance withrespect to the exposure light, and the phase adjusting film has arelatively high transmittance with respect to the exposure light, thephase adjusting film in a formation region for the semi-light-shieldingportion has a thickness that transmits the exposure light in a samephase as that of the light-transmitting portion, and the phase adjustingfilm in a formation region for the peripheral portion has a thicknessthat transmits the exposure light in a phase opposite to that of thelight-transmitting portion.
 12. The photomask according to claim 10,wherein the semi-light-shielding film has a phase adjusting film formedon the transparent substrate and a transmittance adjusting film formedonly on the phase adjusting film in the semi-light-shielding portionformation region, the transmittance adjusting film transmits theexposure light in a same phase as that of the light-transmitting portionand has a relatively low transmittance with respect to the exposurelight, and the phase adjusting film has a relatively high transmittancewith respect to the exposure light, the phase adjusting film in aformation region for the semi-light-shielding portion has a thicknessthat transmits the exposure light in a same phase as that of thelight-transmitting portion, and the phase adjusting film in a formationregion for the peripheral portion has a thickness that transmits theexposure light in a phase opposite to that of the light-transmittingportion.
 13. The photomask according to claim 10, wherein the peripheralportion is in contact with the light-transmitting portion.
 14. Thephotomask according to claim 10, wherein the peripheral portion isspaced apart from the light-transmitting portion by a predetermineddistance.
 15. The photomask according to claim 10, wherein atransmittance of the semi-light-shielding portion with respect to theexposure light is 6% or more and 15% or less.
 16. A method for forming apattern that uses the photomask according to claim 10, comprising thesteps of: forming a resist film on a substrate; irradiating the resistfilm with the exposure light via the photomask, and developing theresist film irradiated with the exposure light so as to pattern theresist film.
 17. The method for forming a pattern according to claim 16,off-axis illumination is used in the step of irradiating the resist filmwith the exposure light.
 18. A photomask comprising on a transparentsubstrate: a semi-light-shielding portion having a light-shieldingproperty with respect to exposure light: a light-transmitting portionsurrounded by the semi-light-shielding portion and having alight-transmitting property with respect to exposure light: and aperipheral portion surrounded by the semi-light-shielding portion andpositioned in a periphery of the light-transmitting portion, wherein thesemi-light-shielding portion and the light-transmitting portion transmitthe exposure light in a same phase, the peripheral portion transmits theexposure light in a phase opposite to that of the semi-light-shieldingportion and the light-transmitting portion, a surface of the transparentsubstrate in a formation region for the light-transmitting portion isexposed, a semi-light-shielding film that has a transmittance thatallows the exposure light to be transmitted partially and transmits theexposure light in a same phase as that of the light-transmitting portionis formed on the transparent substrate in the semi-light-shieldingportion, and the transparent substrate in a formation region for theperipheral portion is dug down such that a thickness thereof is such anextent that the exposure light is transmitted in a phase opposite tothat of the light-transmitting portion.
 19. The photomask according toclaim 18, wherein the semi-light-shielding film has a transmittanceadjusting film formed on the transparent substrate and a phase adjustingfilm formed on the transmittance adjusting film, the transmittanceadjusting film has a relatively low transmittance with respect to theexposure light, and the phase adjusting film has a relatively hightransmittance with respect to the exposure light.
 20. The photomaskaccording to claim 18, wherein the peripheral portion is in contact withthe light-transmitting portion.
 21. The photomask according to claim 18,wherein the peripheral portion is spaced apart from thelight-transmitting portion by a predetermined distance.
 22. Thephotomask according to claim 18, wherein a transmittance of thesemi-light-shielding portion with respect to the exposure light is 6% ormore and 15% or less.
 23. A method for forming a pattern that uses thephotomask according to claim 18, comprising the steps of: forming aresist film on a substrate; irradiating the resist film with theexposure light via the photomask, and developing the resist filmirradiated with the exposure light so as to pattern the resist film. 24.The method for forming a pattern according to claim 23, off-axisillumination is used in the step of irradiating the resist film with theexposure light.
 25. A method for producing a photomask comprising: asemi-light-shielding portion having a light-shielding property withrespect to exposure light: a light-transmitting portion surrounded bythe semi-light-shielding portion and having a light-transmittingproperty with respect to exposure light: and a peripheral portionsurrounded by the semi-light-shielding portion and positioned in aperiphery of the light-transmitting portion on a transparent substrate,the method comprising: a first step of forming a first phase shift filmthat transmits the exposure light in a phase opposite to that of thelight-transmitting portion on the transparent substrate, and a secondstep of forming a second phase shift film that transmits the exposurelight in a phase opposite to that of the light-transmitting portion onthe first phase shift film, a third step of removing the second phaseshift film in a formation region for the light-transmitting portion anda formation region for the peripheral portion, and a fourth step ofremoving the first phase shift film in the light-transmitting portionformation region after the third step, wherein a multilayered structureof the first phase shift film and the second phase shift film formed onthe transparent substrate in the semi-light-shielding portion formationregion has a transmittance that allows the exposure light to betransmitted partially and transmits the exposure light in a same phaseas that of the light-transmitting portion.
 26. The photomask accordingto claim 25, wherein a transmittance of the semi-light-shielding portionwith respect to the exposure light is 6% or more and 15% or less.
 27. Amethod for producing a photomask comprising: a semi-light-shieldingportion having a light-shielding property with respect to exposurelight: a light-transmitting portion surrounded by thesemi-light-shielding portion and having a light-transmitting propertywith respect to exposure light: and a peripheral portion surrounded bythe semi-light-shielding portion and positioned in a periphery of thelight-transmitting portion on a transparent substrate, the methodcomprising: a first step of forming a first phase shift film thattransmits the exposure light in a phase opposite to that of thelight-transmitting portion on the transparent substrate, and a secondstep of forming a second phase shift film that transmits the exposurelight in a phase opposite to that of the light-transmitting portion onthe first phase shift film, a third step of removing the second phaseshift film in a formation region for the peripheral portion, and afourth step of removing the second phase shift film and the first phaseshift film in the light-transmitting portion formation regionsequentially after the third step, wherein a multilayered structure ofthe first phase shift film and the second phase shift film formed on thetransparent substrate in the semi-light-shielding portion formationregion has a transmittance that allows the exposure light to betransmitted partially and transmits the exposure light in a same phaseas that of the light-transmitting portion.
 28. The photomask accordingto claim 27, wherein a transmittance of the semi-light-shielding portionwith respect to the exposure light is 6% or more and 15% or less.